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Re: [PATCH] BZ #14649: Add multiarch FMA support to x86-64 libm
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Andreas Jaeger <aj at suse dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Mon, 1 Oct 2012 11:49:32 -0700
- Subject: Re: [PATCH] BZ #14649: Add multiarch FMA support to x86-64 libm
- References: <20121001151458.GB14836@gmail.com><5069D946.8070408@suse.com>
On Mon, Oct 1, 2012 at 10:56 AM, Andreas Jaeger <aj@suse.com> wrote:
> On 10/01/2012 05:14 PM, H.J. Lu wrote:
>>
>> Hi,
>>
>> This patch adds multiarch FMA support to x86-64 libm. Tested on
>> FMA machine. OK for master?
>
>
> What kind of performance benefits does it bring us? Are you sure that all
I don't have any performance numbers. My patch just
enables FMA optimization, similar to FMA4 optimization.
> the functions you enhance are really using fma and thus benefit from the
> change?
Not all FMA/FMA4 functions have FMA/FMA4 instructions. We should
take a look and use AVX functions instead.
> Btw. are there any processors that have both fma variants in hardware - or
> is it at most one of them?
>
I think some AMD processors support both FMA and FMA4. But Intel
processors only support FMA. My patch follows s_fma.c which prefers
FMA over FMA4.
--
H.J.