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Re: [PATCH] BZ #14649: Add multiarch FMA support to x86-64 libm
On 10/01/2012 08:49 PM, H.J. Lu wrote:
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.
Could you test at least one of these functions to see whether it makes a
difference at all, please?
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.
So, let's only add those functions that really benefit from this.
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.
Hope that's the right thing ;)
Andreas
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