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Re: [PATCH] Change PRED_LOOP_EXIT from 85 to 92
- From: Richard Sandiford <richard dot sandiford at linaro dot org>
- To: Segher Boessenkool <segher at kernel dot crashing dot org>
- Cc: David Esparza <david dot esparza dot borquez at intel dot com>, gcc-patches at gcc dot gnu dot org
- Date: Sun, 24 Dec 2017 09:12:56 +0000
- Subject: Re: [PATCH] Change PRED_LOOP_EXIT from 85 to 92
- Authentication-results: sourceware.org; auth=none
- References: <20171222225347.18748-1-david.esparza.borquez@intel.com> <20171223220816.GG10515@gate.crashing.org>
Segher Boessenkool <segher@kernel.crashing.org> writes:
> On Fri, Dec 22, 2017 at 04:53:47PM -0600, David Esparza wrote:
>> With a value of 85 GCC has a CPU performance degradation of 11%,
>> reverting PRED_LOOP_EXIT to 92 this degradation disappear.
>> Those values where measured by running c-ray ray-tracer that is a
>> floating point benchmark that runs out of L1 cache.
>
> Why is this single benchmark more important than everything else?
>
> https://patchwork.ozlabs.org/patch/637073/
"Everything" else? :-) It sounds from Andrew's reply like it wasn't
a win on other benchmarks too.
Neither covering message has really explained why the previous value was
too low/high, but maybe that's just the way it goes with these tuning
parameters...
Thanks,
Richard