This is the mail archive of the mailing list for the glibc project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH 00/10] Optimized math routines

On 09/07/18 15:26, Adhemerval Zanella wrote:
On 09/07/2018 10:34, Szabolcs Nagy wrote:
On 09/07/18 14:09, Adhemerval Zanella wrote:
On 09/07/2018 09:15, Szabolcs Nagy wrote:
built and tested on a power8 machine now, glibc math
tests pass (except for an unrelated fmal failure),
benchmark improvements are consistent with aarch64/x86_64,
but it was a shared access machine so i won't post exact
numbers, sincosf improved a bit too, sinf/cosf didn't
(apparently powerpc has its own implementation).

PowerPC sinf/cosf uses the same algorithm used on x86, I presume
it would be a gain to generic implementation as well.

you mean the new implementation would be better or the
target specific one?

new implementation has better latency on this particular
powerpc machine than the target specific code, but
throughput is worse sometimes (using the default 0

I did not measure, but I would expect.  PowerPC uses an different
implementation for generic code (s_sinf-ppc64.c) so comparing against
it maybe misleading (since it use the old implementation still).

i'm comparing two glibc builds, they both still use the
same (old) code for sinf/cosf so there is nothing misleading.

the sincosf code is generic though and the new implementation
does show some speedup.

I am not sure which compiler you used for evaluation, but at least
Ubuntu 16.04 one (gcc 5.4) does not use POWER8 ISA as default and
even with -mcpu=power8 it generates subpar code.  I will try to
check with a GCC 7.1 (but as for your environment, I am using
a shared machine, although it I think I might get slight better
results because it uses a micro-partition).

i built a gcc 7.3.0 toolchain, the host toolchain would
not be able to build glibc (gcc-4.8), same for the host
make (3.82). (it's a gcc build farm machine)

For PREFER_FLOAT_COMPARISON, do we use this on glibc? I think
it is only enabled on optimized-routines, isn't it?

it is disabled by default, it is there so targets can enable
it if float compares are faster than using the representation,
currently disabled everywhere in glibc.
(i don't want to change that setting now, that case can
be tweaked later)

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]