Re: [PATCH 00/10] Optimized math routines

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

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
> setting for PREFER_FLOAT_COMPARISON).

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 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).

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