[PATCH v5 6/6] elf: Optimize _dl_new_hash in dl-new-hash.h
Adhemerval Zanella
adhemerval.zanella@linaro.org
Tue May 10 11:58:57 GMT 2022
On 09/05/2022 14:17, Noah Goldstein via Libc-alpha wrote:
> Unroll slightly and enforce good instruction scheduling. This improves
> performance on out-of-order machines. Note the unrolling allows
> for pipelined multiplies which helps a bit, but most of the gain
> is from enforcing better instruction scheduling for more ILP.
> Unrolling further started to induce slowdowns for sizes [0, 4]
> but can help the loop so if larger sizes are the target further
> unrolling can be beneficial.
>
> Results for _dl_new_hash
> Benchmarked on Tigerlake: 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz
>
> Time as Geometric Mean of N=25 runs
> Geometric of all benchmark New / Old: 0.791
> type, length, New Time, Old Time, New Time / Old Time
> fixed, 0, 0.641, 0.658, 0.974
> fixed, 1, 1.888, 1.883, 1.003
> fixed, 2, 2.712, 2.833, 0.957
> fixed, 3, 3.314, 3.739, 0.886
> fixed, 4, 4.316, 4.866, 0.887
> fixed, 5, 5.16, 5.966, 0.865
> fixed, 6, 5.986, 7.241, 0.827
> fixed, 7, 7.264, 8.435, 0.861
> fixed, 8, 8.052, 9.846, 0.818
> fixed, 9, 9.369, 11.316, 0.828
> fixed, 10, 10.256, 12.925, 0.794
> fixed, 11, 12.191, 14.546, 0.838
> fixed, 12, 12.667, 15.92, 0.796
> fixed, 13, 14.442, 17.465, 0.827
> fixed, 14, 14.808, 18.981, 0.78
> fixed, 15, 16.244, 20.565, 0.79
> fixed, 16, 17.166, 22.044, 0.779
> fixed, 32, 35.447, 50.558, 0.701
> fixed, 64, 86.479, 134.529, 0.643
> fixed, 128, 155.453, 287.527, 0.541
> fixed, 256, 302.57, 593.64, 0.51
> random, 2, 11.168, 10.61, 1.053
> random, 4, 13.308, 13.53, 0.984
> random, 8, 16.579, 19.437, 0.853
> random, 16, 21.292, 24.776, 0.859
> random, 32, 30.56, 35.906, 0.851
> random, 64, 49.249, 68.577, 0.718
> random, 128, 81.845, 140.664, 0.582
> random, 256, 152.517, 292.204, 0.522
>
> Co-authored-by: Alexander Monakov <amonakov@ispras.ru>
Buildbot failed to build it [1]:
make[2]: Entering directory '/glibc/elf'
gcc -m32 dl-lookup.c -c -std=gnu11 -fgnu89-inline -g -O2 -Wall -Wwrite-strings -Wundef -Werror -fmerge-all-constants -frounding-math -fno-stack-protector -fno-common -Wstrict-prototypes -Wold-style-definition -fmath-errno -fPIC -fno-stack-protector -DSTACK_PROTECTOR_LEVEL=0 -Wa,-mtune=i686 -mno-sse -mno-mmx -mfpmath=387 -fexceptions -fasynchronous-unwind-tables -ftls-model=initial-exec -I../include -I/build/elf -I/build -I../sysdeps/unix/sysv/linux/i386/i686 -I../sysdeps/i386/i686/nptl -I../sysdeps/unix/sysv/linux/i386 -I../sysdeps/unix/sysv/linux/x86/include -I../sysdeps/unix/sysv/linux/x86 -I../sysdeps/x86/nptl -I../sysdeps/i386/nptl -I../sysdeps/unix/sysv/linux/include -I../sysdeps/unix/sysv/linux -I../sysdeps/nptl -I../sysdeps/pthread -I../sysdeps/gnu -I../sysdeps/unix/inet -I../sysdeps/unix/sysv -I../sysdeps/unix/i386 -I../sysdeps/unix -I../sysdeps/posix -I../sysdeps/i386/i686/fpu/multiarch -I../sysdeps/i386/i686/fpu -I../sysdeps/i386/i686/multiarch -I../sysdeps/i386/i686 -I../sysdeps/i386/fpu -I../sysdeps/x86/fpu -I../sysdeps/i386 -I../sysdeps/x86/include -I../sysdeps/x86 -I../sysdeps/wordsize-32 -I../sysdeps/ieee754/float128 -I../sysdeps/ieee754/ldbl-96/include -I../sysdeps/ieee754/ldbl-96 -I../sysdeps/ieee754/dbl-64 -I../sysdeps/ieee754/flt-32 -I../sysdeps/ieee754 -I../sysdeps/generic -I.. -I../libio -I. -D_LIBC_REENTRANT -include /build/libc-modules.h -DMODULE_NAME=rtld -include ../include/libc-symbols.h -DPIC -DSHARED -DTOP_NAMESPACE=glibc -o /build/elf/dl-lookup.os -MD -MP -MF /build/elf/dl-lookup.os.dt -MT /build/elf/dl-lookup.os
In file included from dl-lookup.c:27:
./dl-new-hash.h: In function '_dl_new_hash':
./dl-new-hash.h:30:28: error: pointer targets in initialization of 'const unsigned char *' from 'const char *' differ in signedness [-Werror=pointer-sign]
30 | const unsigned char *s = signed_s;
| ^~~~~~~~
cc1: all warnings being treated as errors
make[2]: *** [../o-iterator.mk:9: /build/elf/dl-lookup.os] Error 1
gcc -m32 dl-lookup.c -c -std=gnu11 -fgnu89-inline -g -O2 -Wall -Wwrite-strings -Wundef -Werror -fmerge-all-constants -frounding-math -fno-stack-protector -fno-common -Wstrict-prototypes -Wold-style-definition -fmath-errno -fpie -fno-stack-protector -DSTACK_PROTECTOR_LEVEL=0 -Wa,-mtune=i686 -fexceptions -fasynchronous-unwind-tables -ftls-model=initial-exec -I../include -I/build/elf -I/build -I../sysdeps/unix/sysv/linux/i386/i686 -I../sysdeps/i386/i686/nptl -I../sysdeps/unix/sysv/linux/i386 -I../sysdeps/unix/sysv/linux/x86/include -I../sysdeps/unix/sysv/linux/x86 -I../sysdeps/x86/nptl -I../sysdeps/i386/nptl -I../sysdeps/unix/sysv/linux/include -I../sysdeps/unix/sysv/linux -I../sysdeps/nptl -I../sysdeps/pthread -I../sysdeps/gnu -I../sysdeps/unix/inet -I../sysdeps/unix/sysv -I../sysdeps/unix/i386 -I../sysdeps/unix -I../sysdeps/posix -I../sysdeps/i386/i686/fpu/multiarch -I../sysdeps/i386/i686/fpu -I../sysdeps/i386/i686/multiarch -I../sysdeps/i386/i686 -I../sysdeps/i386/fpu -I../sysdeps/x86/fpu -I../sysdeps/i386 -I../sysdeps/x86/include -I../sysdeps/x86 -I../sysdeps/wordsize-32 -I../sysdeps/ieee754/float128 -I../sysdeps/ieee754/ldbl-96/include -I../sysdeps/ieee754/ldbl-96 -I../sysdeps/ieee754/dbl-64 -I../sysdeps/ieee754/flt-32 -I../sysdeps/ieee754 -I../sysdeps/generic -I.. -I../libio -I. -D_LIBC_REENTRANT -include /build/libc-modules.h -DMODULE_NAME=libc -include ../include/libc-symbols.h -DPIC -DTOP_NAMESPACE=glibc -o /build/elf/dl-lookup.o -MD -MP -MF /build/elf/dl-lookup.o.dt -MT /build/elf/dl-lookup.o
In file included from dl-lookup.c:27:
./dl-new-hash.h: In function '_dl_new_hash':
./dl-new-hash.h:30:28: error: pointer targets in initialization of 'const unsigned char *' from 'const char *' differ in signedness [-Werror=pointer-sign]
30 | const unsigned char *s = signed_s;
| ^~~~~~~~
[1] https://www.delorie.com/trybots/32bit/9123/make.tail.txt
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