[PATCH v3 1/3] x86/string: Factor out large memmove implemention to seperate file
Sunil Pandey
skpgkp2@gmail.com
Thu Nov 27 01:18:33 GMT 2025
Hi Noah,
Looking into bugzilla https://sourceware.org/bugzilla/show_bug.cgi?id=32475
Can you please modify patch to just address the issue listed in the bug,
without any change on Intel
processors. As far as I know, we don't have any perf issue on Intel side
and patch is regressing on
newer processors. On SPR this patch has no performance impact.
--Sunil
On Tue, Nov 25, 2025 at 6:42 PM Noah Goldstein <goldstein.w.n@gmail.com>
wrote:
> On Tue, Nov 25, 2025 at 8:44 PM Noah Goldstein <goldstein.w.n@gmail.com>
> wrote:
> >
> > On Tue, Nov 25, 2025 at 10:37 AM Sunil Pandey <skpgkp2@gmail.com> wrote:
> > >
> > >
> > >
> > > On Thu, Nov 20, 2025 at 3:14 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > >>
> > >> On Fri, Nov 21, 2025 at 1:41 AM Sunil Pandey <skpgkp2@gmail.com>
> wrote:
> > >> >
> > >> >
> > >> >
> > >> > On Sat, Nov 15, 2025 at 1:45 AM Noah Goldstein <
> goldstein.w.n@gmail.com> wrote:
> > >> >>
> > >> >> On Sat, Nov 15, 2025 at 4:41 AM Noah Goldstein <
> goldstein.w.n@gmail.com> wrote:
> > >> >> >
> > >> >> > On Sat, Nov 15, 2025 at 4:33 AM Noah Goldstein <
> goldstein.w.n@gmail.com> wrote:
> > >> >> > >
> > >> >> > > This is to enable us to support multiple large (size greater
> than
> > >> >> > > non-temporal threshold) implementations.
> > >> >> > >
> > >> >> > > This patch has no affect on the resulting libc.so library.
> > >> >> > > ---
> > >> >> > > .../memmove-vec-large-page-unrolled.S | 272
> ++++++++++++++++++
> > >> >> > > .../multiarch/memmove-vec-unaligned-erms.S | 272
> +-----------------
> > >> >> > > 2 files changed, 279 insertions(+), 265 deletions(-)
> > >> >> > > create mode 100644
> sysdeps/x86_64/multiarch/memmove-vec-large-page-unrolled.S
> > >> >> > >
> > >> >> > > diff --git
> a/sysdeps/x86_64/multiarch/memmove-vec-large-page-unrolled.S
> b/sysdeps/x86_64/multiarch/memmove-vec-large-page-unrolled.S
> > >> >> > > new file mode 100644
> > >> >> > > index 0000000000..b5b4593279
> > >> >> > > --- /dev/null
> > >> >> > > +++
> b/sysdeps/x86_64/multiarch/memmove-vec-large-page-unrolled.S
> > >> >> > > @@ -0,0 +1,272 @@
> > >> >> > > +#ifdef MEMMOVE_LARGE_IMPL
> > >> >> > > +# error "Multiple large memmove impls included!"
> > >> >> > > +#endif
> > >> >> > > +#define MEMMOVE_LARGE_IMPL 1
> > >> >> > > +
> > >> >> > > +/* Copies large regions by copying multiple pages at once.
> This is
> > >> >> > > + beneficial on some older Intel hardware (Broadwell,
> Skylake, and
> > >> >> > > + Icelake).
> > >> >> > > + 1. If size < 16 * __x86_shared_non_temporal_threshold and
> > >> >> > > + source and destination do not page alias, copy from 2
> pages
> > >> >> > > + at once using non-temporal stores. Page aliasing in
> this case is
> > >> >> > > + considered true if destination's page alignment -
> sources' page
> > >> >> > > + alignment is less than 8 * VEC_SIZE.
> > >> >> > > + 2. If size >= 16 * __x86_shared_non_temporal_threshold or
> source
> > >> >> > > + and destination do page alias copy from 4 pages at once
> using
> > >> >> > > + non-temporal stores. */
> > >> >> > > +
> > >> >> > > +#ifndef LOG_PAGE_SIZE
> > >> >> > > +# define LOG_PAGE_SIZE 12
> > >> >> > > +#endif
> > >> >> > > +
> > >> >> > > +#if PAGE_SIZE != (1 << LOG_PAGE_SIZE)
> > >> >> > > +# error Invalid LOG_PAGE_SIZE
> > >> >> > > +#endif
> > >> >> > > +
> > >> >> > > +/* Byte per page for large_memcpy inner loop. */
> > >> >> > > +#if VEC_SIZE == 64
> > >> >> > > +# define LARGE_LOAD_SIZE (VEC_SIZE * 2)
> > >> >> > > +#else
> > >> >> > > +# define LARGE_LOAD_SIZE (VEC_SIZE * 4)
> > >> >> > > +#endif
> > >> >> > > +
> > >> >> > > +/* Amount to shift __x86_shared_non_temporal_threshold by for
> > >> >> > > + bound for memcpy_large_4x. This is essentially use to to
> > >> >> > > + indicate that the copy is far beyond the scope of L3
> > >> >> > > + (assuming no user config x86_non_temporal_threshold) and to
> > >> >> > > + use a more aggressively unrolled loop. NB: before
> > >> >> > > + increasing the value also update initialization of
> > >> >> > > + x86_non_temporal_threshold. */
> > >> >> > > +#ifndef LOG_4X_MEMCPY_THRESH
> > >> >> > > +# define LOG_4X_MEMCPY_THRESH 4
> > >> >> > > +#endif
> > >> >> > > +
> > >> >> > > +#if LARGE_LOAD_SIZE == (VEC_SIZE * 2)
> > >> >> > > +# define LOAD_ONE_SET(base, offset, vec0, vec1, ...) \
> > >> >> > > + VMOVU (offset)base, vec0; \
> > >> >> > > + VMOVU ((offset) + VEC_SIZE)base, vec1;
> > >> >> > > +# define STORE_ONE_SET(base, offset, vec0, vec1, ...) \
> > >> >> > > + VMOVNT vec0, (offset)base; \
> > >> >> > > + VMOVNT vec1, ((offset) + VEC_SIZE)base;
> > >> >> > > +#elif LARGE_LOAD_SIZE == (VEC_SIZE * 4)
> > >> >> > > +# define LOAD_ONE_SET(base, offset, vec0, vec1, vec2, vec3)
> \
> > >> >> > > + VMOVU (offset)base, vec0; \
> > >> >> > > + VMOVU ((offset) + VEC_SIZE)base, vec1; \
> > >> >> > > + VMOVU ((offset) + VEC_SIZE * 2)base, vec2; \
> > >> >> > > + VMOVU ((offset) + VEC_SIZE * 3)base, vec3;
> > >> >> > > +# define STORE_ONE_SET(base, offset, vec0, vec1, vec2, vec3)
> \
> > >> >> > > + VMOVNT vec0, (offset)base; \
> > >> >> > > + VMOVNT vec1, ((offset) + VEC_SIZE)base; \
> > >> >> > > + VMOVNT vec2, ((offset) + VEC_SIZE * 2)base; \
> > >> >> > > + VMOVNT vec3, ((offset) + VEC_SIZE * 3)base;
> > >> >> > > +#else
> > >> >> > > +# error Invalid LARGE_LOAD_SIZE
> > >> >> > > +#endif
> > >> >> > > +
> > >> >> > > + .p2align 4,, 10
> > >> >> > > +#if (defined USE_MULTIARCH || VEC_SIZE == 16) && IS_IN (libc)
> > >> >> > > +L(large_memcpy_check):
> > >> >> > > + /* Entry from L(large_memcpy_2x) has a redundant load
> of
> > >> >> > > + __x86_shared_non_temporal_threshold(%rip).
> L(large_memcpy_2x)
> > >> >> > > + is only use for the non-erms memmove which is
> generally less
> > >> >> > > + common. */
> > >> >> > > +L(large_memcpy):
> > >> >> > > + mov __x86_shared_non_temporal_threshold(%rip),
> %R11_LP
> > >> >> > > + cmp %R11_LP, %RDX_LP
> > >> >> > > + jb L(more_8x_vec_check)
> > >> >> > > + /* To reach this point it is impossible for dst > src
> and
> > >> >> > > + overlap. Remaining to check is src > dst and
> overlap. rcx
> > >> >> > > + already contains dst - src. Negate rcx to get src -
> dst. If
> > >> >> > > + length > rcx then there is overlap and forward copy
> is best. */
> > >> >> > > + negq %rcx
> > >> >> > > + cmpq %rcx, %rdx
> > >> >> > > + ja L(more_8x_vec_forward)
> > >> >> > > +
> > >> >> > > + /* Cache align destination. First store the first 64
> bytes then
> > >> >> > > + adjust alignments. */
> > >> >> > > +
> > >> >> > > + /* First vec was also loaded into VEC(0). */
> > >> >> > > +# if VEC_SIZE < 64
> > >> >> > > + VMOVU VEC_SIZE(%rsi), %VMM(1)
> > >> >> > > +# if VEC_SIZE < 32
> > >> >> > > + VMOVU (VEC_SIZE * 2)(%rsi), %VMM(2)
> > >> >> > > + VMOVU (VEC_SIZE * 3)(%rsi), %VMM(3)
> > >> >> > > +# endif
> > >> >> > > +# endif
> > >> >> > > + VMOVU %VMM(0), (%rdi)
> > >> >> > > +# if VEC_SIZE < 64
> > >> >> > > + VMOVU %VMM(1), VEC_SIZE(%rdi)
> > >> >> > > +# if VEC_SIZE < 32
> > >> >> > > + VMOVU %VMM(2), (VEC_SIZE * 2)(%rdi)
> > >> >> > > + VMOVU %VMM(3), (VEC_SIZE * 3)(%rdi)
> > >> >> > > +# endif
> > >> >> > > +# endif
> > >> >> > > +
> > >> >> > > + /* Adjust source, destination, and size. */
> > >> >> > > + movq %rdi, %r8
> > >> >> > > + andq $63, %r8
> > >> >> > > + /* Get the negative of offset for alignment. */
> > >> >> > > + subq $64, %r8
> > >> >> > > + /* Adjust source. */
> > >> >> > > + subq %r8, %rsi
> > >> >> > > + /* Adjust destination which should be aligned now. */
> > >> >> > > + subq %r8, %rdi
> > >> >> > > + /* Adjust length. */
> > >> >> > > + addq %r8, %rdx
> > >> >> > > +
> > >> >> > > + /* Test if source and destination addresses will
> alias. If they
> > >> >> > > + do the larger pipeline in large_memcpy_4x
> alleviated the
> > >> >> > > + performance drop. */
> > >> >> > > +
> > >> >> > > + /* ecx contains -(dst - src). not ecx will return dst
> - src - 1
> > >> >> > > + which works for testing aliasing. */
> > >> >> > > + notl %ecx
> > >> >> > > + movq %rdx, %r10
> > >> >> > > + testl $(PAGE_SIZE - VEC_SIZE * 8), %ecx
> > >> >> > > + jz L(large_memcpy_4x)
> > >> >> > > +
> > >> >> > > + /* r11 has __x86_shared_non_temporal_threshold. Shift
> it left
> > >> >> > > + by LOG_4X_MEMCPY_THRESH to get L(large_memcpy_4x)
> threshold. */
> > >> >> > > + shlq $LOG_4X_MEMCPY_THRESH, %r11
> > >> >> > > + cmp %r11, %rdx
> > >> >> > > + jae L(large_memcpy_4x)
> > >> >> > > +
> > >> >> > > + /* edx will store remainder size for copying tail. */
> > >> >> > > + andl $(PAGE_SIZE * 2 - 1), %edx
> > >> >> > > + /* r10 stores outer loop counter. */
> > >> >> > > + shrq $(LOG_PAGE_SIZE + 1), %r10
> > >> >> > > + /* Copy 4x VEC at a time from 2 pages. */
> > >> >> > > + .p2align 4
> > >> >> > > +L(loop_large_memcpy_2x_outer):
> > >> >> > > + /* ecx stores inner loop counter. */
> > >> >> > > + movl $(PAGE_SIZE / LARGE_LOAD_SIZE), %ecx
> > >> >> > > +L(loop_large_memcpy_2x_inner):
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PREFETCHED_LOAD_SIZE)
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PREFETCHED_LOAD_SIZE * 2)
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PAGE_SIZE +
> PREFETCHED_LOAD_SIZE)
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PAGE_SIZE +
> PREFETCHED_LOAD_SIZE * 2)
> > >> >> > > + /* Load vectors from rsi. */
> > >> >> > > + LOAD_ONE_SET ((%rsi), 0, %VMM(0), %VMM(1), %VMM(2),
> %VMM(3))
> > >> >> > > + LOAD_ONE_SET ((%rsi), PAGE_SIZE, %VMM(4), %VMM(5),
> %VMM(6), %VMM(7))
> > >> >> > > + subq $-LARGE_LOAD_SIZE, %rsi
> > >> >> > > + /* Non-temporal store vectors to rdi. */
> > >> >> > > + STORE_ONE_SET ((%rdi), 0, %VMM(0), %VMM(1), %VMM(2),
> %VMM(3))
> > >> >> > > + STORE_ONE_SET ((%rdi), PAGE_SIZE, %VMM(4), %VMM(5),
> %VMM(6), %VMM(7))
> > >> >> > > + subq $-LARGE_LOAD_SIZE, %rdi
> > >> >> > > + decl %ecx
> > >> >> > > + jnz L(loop_large_memcpy_2x_inner)
> > >> >> > > + addq $PAGE_SIZE, %rdi
> > >> >> > > + addq $PAGE_SIZE, %rsi
> > >> >> > > + decq %r10
> > >> >> > > + jne L(loop_large_memcpy_2x_outer)
> > >> >> > > + sfence
> > >> >> > > +
> > >> >> > > + /* Check if only last 4 loads are needed. */
> > >> >> > > + cmpl $(VEC_SIZE * 4), %edx
> > >> >> > > + jbe L(large_memcpy_2x_end)
> > >> >> > > +
> > >> >> > > + /* Handle the last 2 * PAGE_SIZE bytes. */
> > >> >> > > +L(loop_large_memcpy_2x_tail):
> > >> >> > > + /* Copy 4 * VEC a time forward with non-temporal
> stores. */
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PREFETCHED_LOAD_SIZE)
> > >> >> > > + PREFETCH_ONE_SET (1, (%rdi), PREFETCHED_LOAD_SIZE)
> > >> >> > > + VMOVU (%rsi), %VMM(0)
> > >> >> > > + VMOVU VEC_SIZE(%rsi), %VMM(1)
> > >> >> > > + VMOVU (VEC_SIZE * 2)(%rsi), %VMM(2)
> > >> >> > > + VMOVU (VEC_SIZE * 3)(%rsi), %VMM(3)
> > >> >> > > + subq $-(VEC_SIZE * 4), %rsi
> > >> >> > > + addl $-(VEC_SIZE * 4), %edx
> > >> >> > > + VMOVA %VMM(0), (%rdi)
> > >> >> > > + VMOVA %VMM(1), VEC_SIZE(%rdi)
> > >> >> > > + VMOVA %VMM(2), (VEC_SIZE * 2)(%rdi)
> > >> >> > > + VMOVA %VMM(3), (VEC_SIZE * 3)(%rdi)
> > >> >> > > + subq $-(VEC_SIZE * 4), %rdi
> > >> >> > > + cmpl $(VEC_SIZE * 4), %edx
> > >> >> > > + ja L(loop_large_memcpy_2x_tail)
> > >> >> > > +
> > >> >> > > +L(large_memcpy_2x_end):
> > >> >> > > + /* Store the last 4 * VEC. */
> > >> >> > > + VMOVU -(VEC_SIZE * 4)(%rsi, %rdx), %VMM(0)
> > >> >> > > + VMOVU -(VEC_SIZE * 3)(%rsi, %rdx), %VMM(1)
> > >> >> > > + VMOVU -(VEC_SIZE * 2)(%rsi, %rdx), %VMM(2)
> > >> >> > > + VMOVU -VEC_SIZE(%rsi, %rdx), %VMM(3)
> > >> >> > > +
> > >> >> > > + VMOVU %VMM(0), -(VEC_SIZE * 4)(%rdi, %rdx)
> > >> >> > > + VMOVU %VMM(1), -(VEC_SIZE * 3)(%rdi, %rdx)
> > >> >> > > + VMOVU %VMM(2), -(VEC_SIZE * 2)(%rdi, %rdx)
> > >> >> > > + VMOVU %VMM(3), -VEC_SIZE(%rdi, %rdx)
> > >> >> > > + VZEROUPPER_RETURN
> > >> >> > > +
> > >> >> > > + .p2align 4
> > >> >> > > +L(large_memcpy_4x):
> > >> >> > > + /* edx will store remainder size for copying tail. */
> > >> >> > > + andl $(PAGE_SIZE * 4 - 1), %edx
> > >> >> > > + /* r10 stores outer loop counter. */
> > >> >> > > + shrq $(LOG_PAGE_SIZE + 2), %r10
> > >> >> > > + /* Copy 4x VEC at a time from 4 pages. */
> > >> >> > > + .p2align 4
> > >> >> > > +L(loop_large_memcpy_4x_outer):
> > >> >> > > + /* ecx stores inner loop counter. */
> > >> >> > > + movl $(PAGE_SIZE / LARGE_LOAD_SIZE), %ecx
> > >> >> > > +L(loop_large_memcpy_4x_inner):
> > >> >> > > + /* Only one prefetch set per page as doing 4 pages
> give more
> > >> >> > > + time for prefetcher to keep up. */
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PREFETCHED_LOAD_SIZE)
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PAGE_SIZE +
> PREFETCHED_LOAD_SIZE)
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PAGE_SIZE * 2 +
> PREFETCHED_LOAD_SIZE)
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PAGE_SIZE * 3 +
> PREFETCHED_LOAD_SIZE)
> > >> >> > > + /* Load vectors from rsi. */
> > >> >> > > + LOAD_ONE_SET ((%rsi), 0, %VMM(0), %VMM(1), %VMM(2),
> %VMM(3))
> > >> >> > > + LOAD_ONE_SET ((%rsi), PAGE_SIZE, %VMM(4), %VMM(5),
> %VMM(6), %VMM(7))
> > >> >> > > + LOAD_ONE_SET ((%rsi), PAGE_SIZE * 2, %VMM(8), %VMM(9),
> %VMM(10), %VMM(11))
> > >> >> > > + LOAD_ONE_SET ((%rsi), PAGE_SIZE * 3, %VMM(12),
> %VMM(13), %VMM(14), %VMM(15))
> > >> >> > > + subq $-LARGE_LOAD_SIZE, %rsi
> > >> >> > > + /* Non-temporal store vectors to rdi. */
> > >> >> > > + STORE_ONE_SET ((%rdi), 0, %VMM(0), %VMM(1), %VMM(2),
> %VMM(3))
> > >> >> > > + STORE_ONE_SET ((%rdi), PAGE_SIZE, %VMM(4), %VMM(5),
> %VMM(6), %VMM(7))
> > >> >> > > + STORE_ONE_SET ((%rdi), PAGE_SIZE * 2, %VMM(8),
> %VMM(9), %VMM(10), %VMM(11))
> > >> >> > > + STORE_ONE_SET ((%rdi), PAGE_SIZE * 3, %VMM(12),
> %VMM(13), %VMM(14), %VMM(15))
> > >> >> > > + subq $-LARGE_LOAD_SIZE, %rdi
> > >> >> > > + decl %ecx
> > >> >> > > + jnz L(loop_large_memcpy_4x_inner)
> > >> >> > > + addq $(PAGE_SIZE * 3), %rdi
> > >> >> > > + addq $(PAGE_SIZE * 3), %rsi
> > >> >> > > + decq %r10
> > >> >> > > + jne L(loop_large_memcpy_4x_outer)
> > >> >> > > + sfence
> > >> >> > > + /* Check if only last 4 loads are needed. */
> > >> >> > > + cmpl $(VEC_SIZE * 4), %edx
> > >> >> > > + jbe L(large_memcpy_4x_end)
> > >> >> > > +
> > >> >> > > + /* Handle the last 4 * PAGE_SIZE bytes. */
> > >> >> > > +L(loop_large_memcpy_4x_tail):
> > >> >> > > + /* Copy 4 * VEC a time forward with non-temporal
> stores. */
> > >> >> > > + PREFETCH_ONE_SET (1, (%rsi), PREFETCHED_LOAD_SIZE)
> > >> >> > > + PREFETCH_ONE_SET (1, (%rdi), PREFETCHED_LOAD_SIZE)
> > >> >> > > + VMOVU (%rsi), %VMM(0)
> > >> >> > > + VMOVU VEC_SIZE(%rsi), %VMM(1)
> > >> >> > > + VMOVU (VEC_SIZE * 2)(%rsi), %VMM(2)
> > >> >> > > + VMOVU (VEC_SIZE * 3)(%rsi), %VMM(3)
> > >> >> > > + subq $-(VEC_SIZE * 4), %rsi
> > >> >> > > + addl $-(VEC_SIZE * 4), %edx
> > >> >> > > + VMOVA %VMM(0), (%rdi)
> > >> >> > > + VMOVA %VMM(1), VEC_SIZE(%rdi)
> > >> >> > > + VMOVA %VMM(2), (VEC_SIZE * 2)(%rdi)
> > >> >> > > + VMOVA %VMM(3), (VEC_SIZE * 3)(%rdi)
> > >> >> > > + subq $-(VEC_SIZE * 4), %rdi
> > >> >> > > + cmpl $(VEC_SIZE * 4), %edx
> > >> >> > > + ja L(loop_large_memcpy_4x_tail)
> > >> >> > > +
> > >> >> > > +L(large_memcpy_4x_end):
> > >> >> > > + /* Store the last 4 * VEC. */
> > >> >> > > + VMOVU -(VEC_SIZE * 4)(%rsi, %rdx), %VMM(0)
> > >> >> > > + VMOVU -(VEC_SIZE * 3)(%rsi, %rdx), %VMM(1)
> > >> >> > > + VMOVU -(VEC_SIZE * 2)(%rsi, %rdx), %VMM(2)
> > >> >> > > + VMOVU -VEC_SIZE(%rsi, %rdx), %VMM(3)
> > >> >> > > +
> > >> >> > > + VMOVU %VMM(0), -(VEC_SIZE * 4)(%rdi, %rdx)
> > >> >> > > + VMOVU %VMM(1), -(VEC_SIZE * 3)(%rdi, %rdx)
> > >> >> > > + VMOVU %VMM(2), -(VEC_SIZE * 2)(%rdi, %rdx)
> > >> >> > > + VMOVU %VMM(3), -VEC_SIZE(%rdi, %rdx)
> > >> >> > > + VZEROUPPER_RETURN
> > >> >> > > +#endif
> > >> >> > > diff --git
> a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> > >> >> > > index 5cd8a6286e..70d303687c 100644
> > >> >> > > --- a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> > >> >> > > +++ b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> > >> >> > > @@ -34,17 +34,8 @@
> > >> >> > > __x86_rep_movsb_threshold and less than
> > >> >> > > __x86_rep_movsb_stop_threshold, then REP MOVSB will be
> used.
> > >> >> > > 7. If size >= __x86_shared_non_temporal_threshold and
> there is no
> > >> >> > > - overlap between destination and source, use
> non-temporal store
> > >> >> > > - instead of aligned store copying from either 2 or 4
> pages at
> > >> >> > > - once.
> > >> >> > > - 8. For point 7) if size < 16 *
> __x86_shared_non_temporal_threshold
> > >> >> > > - and source and destination do not page alias, copy from
> 2 pages
> > >> >> > > - at once using non-temporal stores. Page aliasing in
> this case is
> > >> >> > > - considered true if destination's page alignment -
> sources' page
> > >> >> > > - alignment is less than 8 * VEC_SIZE.
> > >> >> > > - 9. If size >= 16 * __x86_shared_non_temporal_threshold or
> source
> > >> >> > > - and destination do page alias copy from 4 pages at once
> using
> > >> >> > > - non-temporal stores. */
> > >> >> > > + overlap between destination and source, the exact
> method varies
> > >> >> > > + and is set with MEMMOVE_VEC_LARGE_IMPL". */
> > >> >> > >
> > >> >> > > #include <sysdep.h>
> > >> >> > >
> > >> >> > > @@ -95,31 +86,6 @@
> > >> >> > > # error Unsupported PAGE_SIZE
> > >> >> > > #endif
> > >> >> > >
> > >> >> > > -#ifndef LOG_PAGE_SIZE
> > >> >> > > -# define LOG_PAGE_SIZE 12
> > >> >> > > -#endif
> > >> >> > > -
> > >> >> > > -#if PAGE_SIZE != (1 << LOG_PAGE_SIZE)
> > >> >> > > -# error Invalid LOG_PAGE_SIZE
> > >> >> > > -#endif
> > >> >> > > -
> > >> >> > > -/* Byte per page for large_memcpy inner loop. */
> > >> >> > > -#if VEC_SIZE == 64
> > >> >> > > -# define LARGE_LOAD_SIZE (VEC_SIZE * 2)
> > >> >> > > -#else
> > >> >> > > -# define LARGE_LOAD_SIZE (VEC_SIZE * 4)
> > >> >> > > -#endif
> > >> >> > > -
> > >> >> > > -/* Amount to shift __x86_shared_non_temporal_threshold by for
> > >> >> > > - bound for memcpy_large_4x. This is essentially use to to
> > >> >> > > - indicate that the copy is far beyond the scope of L3
> > >> >> > > - (assuming no user config x86_non_temporal_threshold) and to
> > >> >> > > - use a more aggressively unrolled loop. NB: before
> > >> >> > > - increasing the value also update initialization of
> > >> >> > > - x86_non_temporal_threshold. */
> > >> >> > > -#ifndef LOG_4X_MEMCPY_THRESH
> > >> >> > > -# define LOG_4X_MEMCPY_THRESH 4
> > >> >> > > -#endif
> > >> >> > >
> > >> >> > > /* Avoid short distance rep movsb only with non-SSE vector.
> */
> > >> >> > > #ifndef AVOID_SHORT_DISTANCE_REP_MOVSB
> > >> >> > > @@ -160,26 +126,8 @@
> > >> >> > > # error Unsupported PREFETCH_SIZE!
> > >> >> > > #endif
> > >> >> > >
> > >> >> > > -#if LARGE_LOAD_SIZE == (VEC_SIZE * 2)
> > >> >> > > -# define LOAD_ONE_SET(base, offset, vec0, vec1, ...) \
> > >> >> > > - VMOVU (offset)base, vec0; \
> > >> >> > > - VMOVU ((offset) + VEC_SIZE)base, vec1;
> > >> >> > > -# define STORE_ONE_SET(base, offset, vec0, vec1, ...) \
> > >> >> > > - VMOVNT vec0, (offset)base; \
> > >> >> > > - VMOVNT vec1, ((offset) + VEC_SIZE)base;
> > >> >> > > -#elif LARGE_LOAD_SIZE == (VEC_SIZE * 4)
> > >> >> > > -# define LOAD_ONE_SET(base, offset, vec0, vec1, vec2, vec3) \
> > >> >> > > - VMOVU (offset)base, vec0; \
> > >> >> > > - VMOVU ((offset) + VEC_SIZE)base, vec1; \
> > >> >> > > - VMOVU ((offset) + VEC_SIZE * 2)base, vec2; \
> > >> >> > > - VMOVU ((offset) + VEC_SIZE * 3)base, vec3;
> > >> >> > > -# define STORE_ONE_SET(base, offset, vec0, vec1, vec2, vec3) \
> > >> >> > > - VMOVNT vec0, (offset)base; \
> > >> >> > > - VMOVNT vec1, ((offset) + VEC_SIZE)base; \
> > >> >> > > - VMOVNT vec2, ((offset) + VEC_SIZE * 2)base; \
> > >> >> > > - VMOVNT vec3, ((offset) + VEC_SIZE * 3)base;
> > >> >> > > -#else
> > >> >> > > -# error Invalid LARGE_LOAD_SIZE
> > >> >> > > +#ifndef MEMMOVE_VEC_LARGE_IMPL
> > >> >> > > +# define MEMMOVE_VEC_LARGE_IMPL
> "memmove-vec-large-page-unrolled.S"
> > >> >> > > #endif
> > >> >> > >
> > >> >> > > #ifndef SECTION
> > >> >> > > @@ -426,7 +374,7 @@ L(more_8x_vec):
> > >> >> > > #if (defined USE_MULTIARCH || VEC_SIZE == 16) && IS_IN (libc)
> > >> >> > > /* Check non-temporal store threshold. */
> > >> >> > > cmp __x86_shared_non_temporal_threshold(%rip),
> %RDX_LP
> > >> >> > > - ja L(large_memcpy_2x)
> > >> >> > > + ja L(large_memcpy)
> > >> >> > > #endif
> > >> >> > > /* To reach this point there cannot be overlap and dst
> > src. So
> > >> >> > > check for overlap and src > dst in which case
> correctness
> > >> >> > > @@ -613,7 +561,7 @@ L(movsb):
> > >> >> > > /* If above __x86_rep_movsb_stop_threshold most likely
> is
> > >> >> > > candidate for NT moves as well. */
> > >> >> > > cmp __x86_rep_movsb_stop_threshold(%rip), %RDX_LP
> > >> >> > > - jae L(large_memcpy_2x_check)
> > >> >> > > + jae L(large_memcpy_check)
> > >> >> > > # if AVOID_SHORT_DISTANCE_REP_MOVSB || ALIGN_MOVSB
> > >> >> > > /* Only avoid short movsb if CPU has FSRM. */
> > >> >> > > # if X86_STRING_CONTROL_AVOID_SHORT_DISTANCE_REP_MOVSB < 256
> > >> >> > > @@ -673,214 +621,8 @@ L(skip_short_movsb_check):
> > >> >> > > # endif
> > >> >> > > #endif
> > >> >> > >
> > >> >> > > - .p2align 4,, 10
> > >> >> > > -#if (defined USE_MULTIARCH || VEC_SIZE == 16) && IS_IN (libc)
> > >> >> > > -L(large_memcpy_2x_check):
> > >> >> > > - /* Entry from L(large_memcpy_2x) has a redundant load
> of
> > >> >> > > - __x86_shared_non_temporal_threshold(%rip).
> L(large_memcpy_2x)
> > >> >> > > - is only use for the non-erms memmove which is
> generally less
> > >> >> > > - common. */
> > >> >> > > -L(large_memcpy_2x):
> > >> >> > > - mov __x86_shared_non_temporal_threshold(%rip),
> %R11_LP
> > >> >> > > - cmp %R11_LP, %RDX_LP
> > >> >> > > - jb L(more_8x_vec_check)
> > >> >> > > - /* To reach this point it is impossible for dst > src
> and
> > >> >> > > - overlap. Remaining to check is src > dst and
> overlap. rcx
> > >> >> > > - already contains dst - src. Negate rcx to get src -
> dst. If
> > >> >> > > - length > rcx then there is overlap and forward copy
> is best. */
> > >> >> > > - negq %rcx
> > >> >> > > - cmpq %rcx, %rdx
> > >> >> > > - ja L(more_8x_vec_forward)
> > >> >> > > -
> > >> >> > > - /* Cache align destination. First store the first 64
> bytes then
> > >> >> > > - adjust alignments. */
> > >> >> > > -
> > >> >> > > - /* First vec was also loaded into VEC(0). */
> > >> >> > > -# if VEC_SIZE < 64
> > >> >> > > - VMOVU VEC_SIZE(%rsi), %VMM(1)
> > >> >> > > -# if VEC_SIZE < 32
> > >> >> > > - VMOVU (VEC_SIZE * 2)(%rsi), %VMM(2)
> > >> >> > > - VMOVU (VEC_SIZE * 3)(%rsi), %VMM(3)
> > >> >> > > -# endif
> > >> >> > > -# endif
> > >> >> > > - VMOVU %VMM(0), (%rdi)
> > >> >> > > -# if VEC_SIZE < 64
> > >> >> > > - VMOVU %VMM(1), VEC_SIZE(%rdi)
> > >> >> > > -# if VEC_SIZE < 32
> > >> >> > > - VMOVU %VMM(2), (VEC_SIZE * 2)(%rdi)
> > >> >> > > - VMOVU %VMM(3), (VEC_SIZE * 3)(%rdi)
> > >> >> > > -# endif
> > >> >> > > -# endif
> > >> >> > > +#include MEMMOVE_VEC_LARGE_IMPL
> > >> >> > >
> > >> >> > > - /* Adjust source, destination, and size. */
> > >> >> > > - movq %rdi, %r8
> > >> >> > > - andq $63, %r8
> > >> >> > > - /* Get the negative of offset for alignment. */
> > >> >> > > - subq $64, %r8
> > >> >> > > - /* Adjust source. */
> > >> >> > > - subq %r8, %rsi
> > >> >> > > - /* Adjust destination which should be aligned now. */
> > >> >> > > - subq %r8, %rdi
> > >> >> > > - /* Adjust length. */
> > >> >> > > - addq %r8, %rdx
> > >> >> > > -
> > >> >> > > - /* Test if source and destination addresses will
> alias. If they
> > >> >> > > - do the larger pipeline in large_memcpy_4x
> alleviated the
> > >> >> > > - performance drop. */
> > >> >> > > -
> > >> >> > > - /* ecx contains -(dst - src). not ecx will return dst
> - src - 1
> > >> >> > > - which works for testing aliasing. */
> > >> >> > > - notl %ecx
> > >> >> > > - movq %rdx, %r10
> > >> >> > > - testl $(PAGE_SIZE - VEC_SIZE * 8), %ecx
> > >> >> > > - jz L(large_memcpy_4x)
> > >> >> > > -
> > >> >> > > - /* r11 has __x86_shared_non_temporal_threshold. Shift
> it left
> > >> >> > > - by LOG_4X_MEMCPY_THRESH to get L(large_memcpy_4x)
> threshold.
> > >> >> > > - */
> > >> >> > > - shlq $LOG_4X_MEMCPY_THRESH, %r11
> > >> >> > > - cmp %r11, %rdx
> > >> >> > > - jae L(large_memcpy_4x)
> > >> >> > > -
> > >> >> > > - /* edx will store remainder size for copying tail. */
> > >> >> > > - andl $(PAGE_SIZE * 2 - 1), %edx
> > >> >> > > - /* r10 stores outer loop counter. */
> > >> >> > > - shrq $(LOG_PAGE_SIZE + 1), %r10
> > >> >> > > - /* Copy 4x VEC at a time from 2 pages. */
> > >> >> > > - .p2align 4
> > >> >> > > -L(loop_large_memcpy_2x_outer):
> > >> >> > > - /* ecx stores inner loop counter. */
> > >> >> > > - movl $(PAGE_SIZE / LARGE_LOAD_SIZE), %ecx
> > >> >> > > -L(loop_large_memcpy_2x_inner):
> > >> >> > > - PREFETCH_ONE_SET(1, (%rsi), PREFETCHED_LOAD_SIZE)
> > >> >> > > - PREFETCH_ONE_SET(1, (%rsi), PREFETCHED_LOAD_SIZE * 2)
> > >> >> > > - PREFETCH_ONE_SET(1, (%rsi), PAGE_SIZE +
> PREFETCHED_LOAD_SIZE)
> > >> >> > > - PREFETCH_ONE_SET(1, (%rsi), PAGE_SIZE +
> PREFETCHED_LOAD_SIZE * 2)
> > >> >> > > - /* Load vectors from rsi. */
> > >> >> > > - LOAD_ONE_SET((%rsi), 0, %VMM(0), %VMM(1), %VMM(2),
> %VMM(3))
> > >> >> > > - LOAD_ONE_SET((%rsi), PAGE_SIZE, %VMM(4), %VMM(5),
> %VMM(6), %VMM(7))
> > >> >> > > - subq $-LARGE_LOAD_SIZE, %rsi
> > >> >> > > - /* Non-temporal store vectors to rdi. */
> > >> >> > > - STORE_ONE_SET((%rdi), 0, %VMM(0), %VMM(1), %VMM(2),
> %VMM(3))
> > >> >> > > - STORE_ONE_SET((%rdi), PAGE_SIZE, %VMM(4), %VMM(5),
> %VMM(6), %VMM(7))
> > >> >> > > - subq $-LARGE_LOAD_SIZE, %rdi
> > >> >> > > - decl %ecx
> > >> >> > > - jnz L(loop_large_memcpy_2x_inner)
> > >> >> > > - addq $PAGE_SIZE, %rdi
> > >> >> > > - addq $PAGE_SIZE, %rsi
> > >> >> > > - decq %r10
> > >> >> > > - jne L(loop_large_memcpy_2x_outer)
> > >> >> > > - sfence
> > >> >> > > -
> > >> >> > > - /* Check if only last 4 loads are needed. */
> > >> >> > > - cmpl $(VEC_SIZE * 4), %edx
> > >> >> > > - jbe L(large_memcpy_2x_end)
> > >> >> > > -
> > >> >> > > - /* Handle the last 2 * PAGE_SIZE bytes. */
> > >> >> > > -L(loop_large_memcpy_2x_tail):
> > >> >> > > - /* Copy 4 * VEC a time forward with non-temporal
> stores. */
> > >> >> > > - PREFETCH_ONE_SET (1, (%rsi), PREFETCHED_LOAD_SIZE)
> > >> >> > > - PREFETCH_ONE_SET (1, (%rdi), PREFETCHED_LOAD_SIZE)
> > >> >> > > - VMOVU (%rsi), %VMM(0)
> > >> >> > > - VMOVU VEC_SIZE(%rsi), %VMM(1)
> > >> >> > > - VMOVU (VEC_SIZE * 2)(%rsi), %VMM(2)
> > >> >> > > - VMOVU (VEC_SIZE * 3)(%rsi), %VMM(3)
> > >> >> > > - subq $-(VEC_SIZE * 4), %rsi
> > >> >> > > - addl $-(VEC_SIZE * 4), %edx
> > >> >> > > - VMOVA %VMM(0), (%rdi)
> > >> >> > > - VMOVA %VMM(1), VEC_SIZE(%rdi)
> > >> >> > > - VMOVA %VMM(2), (VEC_SIZE * 2)(%rdi)
> > >> >> > > - VMOVA %VMM(3), (VEC_SIZE * 3)(%rdi)
> > >> >> > > - subq $-(VEC_SIZE * 4), %rdi
> > >> >> > > - cmpl $(VEC_SIZE * 4), %edx
> > >> >> > > - ja L(loop_large_memcpy_2x_tail)
> > >> >> > > -
> > >> >> > > -L(large_memcpy_2x_end):
> > >> >> > > - /* Store the last 4 * VEC. */
> > >> >> > > - VMOVU -(VEC_SIZE * 4)(%rsi, %rdx), %VMM(0)
> > >> >> > > - VMOVU -(VEC_SIZE * 3)(%rsi, %rdx), %VMM(1)
> > >> >> > > - VMOVU -(VEC_SIZE * 2)(%rsi, %rdx), %VMM(2)
> > >> >> > > - VMOVU -VEC_SIZE(%rsi, %rdx), %VMM(3)
> > >> >> > > -
> > >> >> > > - VMOVU %VMM(0), -(VEC_SIZE * 4)(%rdi, %rdx)
> > >> >> > > - VMOVU %VMM(1), -(VEC_SIZE * 3)(%rdi, %rdx)
> > >> >> > > - VMOVU %VMM(2), -(VEC_SIZE * 2)(%rdi, %rdx)
> > >> >> > > - VMOVU %VMM(3), -VEC_SIZE(%rdi, %rdx)
> > >> >> > > - VZEROUPPER_RETURN
> > >> >> > > -
> > >> >> > > - .p2align 4
> > >> >> > > -L(large_memcpy_4x):
> > >> >> > > - /* edx will store remainder size for copying tail. */
> > >> >> > > - andl $(PAGE_SIZE * 4 - 1), %edx
> > >> >> > > - /* r10 stores outer loop counter. */
> > >> >> > > - shrq $(LOG_PAGE_SIZE + 2), %r10
> > >> >> > > - /* Copy 4x VEC at a time from 4 pages. */
> > >> >> > > - .p2align 4
> > >> >> > > -L(loop_large_memcpy_4x_outer):
> > >> >> > > - /* ecx stores inner loop counter. */
> > >> >> > > - movl $(PAGE_SIZE / LARGE_LOAD_SIZE), %ecx
> > >> >> > > -L(loop_large_memcpy_4x_inner):
> > >> >> > > - /* Only one prefetch set per page as doing 4 pages
> give more
> > >> >> > > - time for prefetcher to keep up. */
> > >> >> > > - PREFETCH_ONE_SET(1, (%rsi), PREFETCHED_LOAD_SIZE)
> > >> >> > > - PREFETCH_ONE_SET(1, (%rsi), PAGE_SIZE +
> PREFETCHED_LOAD_SIZE)
> > >> >> > > - PREFETCH_ONE_SET(1, (%rsi), PAGE_SIZE * 2 +
> PREFETCHED_LOAD_SIZE)
> > >> >> > > - PREFETCH_ONE_SET(1, (%rsi), PAGE_SIZE * 3 +
> PREFETCHED_LOAD_SIZE)
> > >> >> > > - /* Load vectors from rsi. */
> > >> >> > > - LOAD_ONE_SET((%rsi), 0, %VMM(0), %VMM(1), %VMM(2),
> %VMM(3))
> > >> >> > > - LOAD_ONE_SET((%rsi), PAGE_SIZE, %VMM(4), %VMM(5),
> %VMM(6), %VMM(7))
> > >> >> > > - LOAD_ONE_SET((%rsi), PAGE_SIZE * 2, %VMM(8), %VMM(9),
> %VMM(10), %VMM(11))
> > >> >> > > - LOAD_ONE_SET((%rsi), PAGE_SIZE * 3, %VMM(12),
> %VMM(13), %VMM(14), %VMM(15))
> > >> >> > > - subq $-LARGE_LOAD_SIZE, %rsi
> > >> >> > > - /* Non-temporal store vectors to rdi. */
> > >> >> > > - STORE_ONE_SET((%rdi), 0, %VMM(0), %VMM(1), %VMM(2),
> %VMM(3))
> > >> >> > > - STORE_ONE_SET((%rdi), PAGE_SIZE, %VMM(4), %VMM(5),
> %VMM(6), %VMM(7))
> > >> >> > > - STORE_ONE_SET((%rdi), PAGE_SIZE * 2, %VMM(8), %VMM(9),
> %VMM(10), %VMM(11))
> > >> >> > > - STORE_ONE_SET((%rdi), PAGE_SIZE * 3, %VMM(12),
> %VMM(13), %VMM(14), %VMM(15))
> > >> >> > > - subq $-LARGE_LOAD_SIZE, %rdi
> > >> >> > > - decl %ecx
> > >> >> > > - jnz L(loop_large_memcpy_4x_inner)
> > >> >> > > - addq $(PAGE_SIZE * 3), %rdi
> > >> >> > > - addq $(PAGE_SIZE * 3), %rsi
> > >> >> > > - decq %r10
> > >> >> > > - jne L(loop_large_memcpy_4x_outer)
> > >> >> > > - sfence
> > >> >> > > - /* Check if only last 4 loads are needed. */
> > >> >> > > - cmpl $(VEC_SIZE * 4), %edx
> > >> >> > > - jbe L(large_memcpy_4x_end)
> > >> >> > > -
> > >> >> > > - /* Handle the last 4 * PAGE_SIZE bytes. */
> > >> >> > > -L(loop_large_memcpy_4x_tail):
> > >> >> > > - /* Copy 4 * VEC a time forward with non-temporal
> stores. */
> > >> >> > > - PREFETCH_ONE_SET (1, (%rsi), PREFETCHED_LOAD_SIZE)
> > >> >> > > - PREFETCH_ONE_SET (1, (%rdi), PREFETCHED_LOAD_SIZE)
> > >> >> > > - VMOVU (%rsi), %VMM(0)
> > >> >> > > - VMOVU VEC_SIZE(%rsi), %VMM(1)
> > >> >> > > - VMOVU (VEC_SIZE * 2)(%rsi), %VMM(2)
> > >> >> > > - VMOVU (VEC_SIZE * 3)(%rsi), %VMM(3)
> > >> >> > > - subq $-(VEC_SIZE * 4), %rsi
> > >> >> > > - addl $-(VEC_SIZE * 4), %edx
> > >> >> > > - VMOVA %VMM(0), (%rdi)
> > >> >> > > - VMOVA %VMM(1), VEC_SIZE(%rdi)
> > >> >> > > - VMOVA %VMM(2), (VEC_SIZE * 2)(%rdi)
> > >> >> > > - VMOVA %VMM(3), (VEC_SIZE * 3)(%rdi)
> > >> >> > > - subq $-(VEC_SIZE * 4), %rdi
> > >> >> > > - cmpl $(VEC_SIZE * 4), %edx
> > >> >> > > - ja L(loop_large_memcpy_4x_tail)
> > >> >> > > -
> > >> >> > > -L(large_memcpy_4x_end):
> > >> >> > > - /* Store the last 4 * VEC. */
> > >> >> > > - VMOVU -(VEC_SIZE * 4)(%rsi, %rdx), %VMM(0)
> > >> >> > > - VMOVU -(VEC_SIZE * 3)(%rsi, %rdx), %VMM(1)
> > >> >> > > - VMOVU -(VEC_SIZE * 2)(%rsi, %rdx), %VMM(2)
> > >> >> > > - VMOVU -VEC_SIZE(%rsi, %rdx), %VMM(3)
> > >> >> > > -
> > >> >> > > - VMOVU %VMM(0), -(VEC_SIZE * 4)(%rdi, %rdx)
> > >> >> > > - VMOVU %VMM(1), -(VEC_SIZE * 3)(%rdi, %rdx)
> > >> >> > > - VMOVU %VMM(2), -(VEC_SIZE * 2)(%rdi, %rdx)
> > >> >> > > - VMOVU %VMM(3), -VEC_SIZE(%rdi, %rdx)
> > >> >> > > - VZEROUPPER_RETURN
> > >> >> > > -#endif
> > >> >> > > END (MEMMOVE_SYMBOL (__memmove, unaligned_erms))
> > >> >> > >
> > >> >> > > #if IS_IN (libc)
> > >> >> > > --
> > >> >> > > 2.43.0
> > >> >> > >
> > >> >> >
> > >> >> > For the entire series:
> > >> >> > I tested this natively on x86_64 when I wrote this, but I no
> longer
> > >> >> > have any x86 machines.
> > >> >> > I re-tested w/ QEMU before re-posting, but I think it would be
> worthwhile if
> > >> >> ... if someone could re-check natively before commit (after review
> has
> > >> >> been completed).
> > >> >
> > >> >
> > >> > Hi Noah,
> > >> >
> > >> > I tested this patch and got geomean regression upto 6% on large
> data size microbenchmark.
> > >> >
> > >> > Thanks,
> > >> > Sunil
> > >>
> > >> Any impact on SPEC CPU?
> > >>
> > >
> > > Spec2017 regression(502.gcc_r , 520.omnetpp_r) on newer AVX-256 system
> after applying 3 patch sets.
> > >
> > > 503.bwaves_r -1%
> > > 507.cactuBSSN_r -1%
> > > 508.namd_r 0%
> > > 510.parest_r 0%
> > > 511.povray_r 0%
> > > 519.lbm_r 0%
> > > 521.wrf_r 0%
> > > 526.blender_r 1%
> > > 527.cam4_r 1%
> > > 538.imagick_r 0%
> > > 544.nab_r 0%
> > > 549.fotonik3d_r 1%
> > > 554.roms_r 0%
> > > 500.perlbench_r 0%
> > > 502.gcc_r -2%
> > > 505.mcf_r 0%
> > > 520.omnetpp_r -3%
> > > 523.xalancbmk_r 1%
> > > 525.x264_r -1%
> > > 531.deepsjeng_r 0%
> > > 541.leela_r 0%
> > > 548.exchange2_r 0%
> > > 557.xz_r -1%
> >
> > That's possibly within the noise, but as discussed, this should be
> > handled in a follow up
> > by adjusting the preferred implementation on whatever newer system you
> > had in mind.
>
>
> Alternatively, you can give me a list of CPUs you would prefer to keep the
> old
> behavior on.
> I do think it should be CPU by CPU w/ strong benchmarks to support it,
> but if you
> want more aggressive continuation of current behavior on Intel machines
> that is
> understandable too.
>
> I will note, before leaving Intel I did do some SPR benchmarks of page
> unrolled
> vs normal loop:
>
>
> https://docs.google.com/spreadsheets/d/1-8M-VNeERLxzsghX3CnYUS09pURckmAJLcUkAzTJaVE/edit?usp=sharing
>
> Comparing NT vs NT_4x. Lower numbers are better.
> (CD is movdir64 just for reference).
>
> The benchmark code does slightly vary from what we have in GLIBC,
> but I take it as evidence that it is not clear we should blindly be
> continuing
> the page unrolled implementation.
>
>
>
> > >
> > > --Sunil
> > >
> > >>
> > >> --
> > >> H.J.
>
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