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Date: Sat, 6 Jun 2015 23:06:08 +0800
From: Lei Zhang <zhanglei.april@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: Interleaving of intrinsics
> On Jun 6, 2015, at 7:47 PM, Solar Designer <solar@...nwall.com> wrote:
>
> Your use of VTune appears to be similar to use of gprof. If you use
> VTune at all, I'd expect you to profile things such as cache misses and
> pipeline stalls, as well as utilization of the CPU's execution units.
> Things that only the CPU vendor's profiler is capable of.
I'll take a further look.
> On Sat, Jun 06, 2015 at 07:38:18PM +0800, Lei Zhang wrote:
>> Same settings as the previous, except for longer run time (--test=20):
>
> Are the benchmark results significantly affected by your use of
> profiling, vs. a non-profiled run? This is very important. In some
> cases, profiling may change performance by an order of magnitude or even
> worse, which means that its results would be of questionable relevance.
From the results of self-test, there's no noticeable penalty in profiling.
>> Use of intrinsics is counted as function calls
>
> That's weird. You need to make sure they haven't, in fact, been turned
> into function calls or the like in this profiling build. If they have,
> performance is probably at a level much worse than what we normally see,
> and if so this is an instance of the problem I mentioned above.
This is indeed weird. The previous experiments were done with gcc. I just profiled an icc build, and the result is vastly different:
Function CPU Time
SSESHA256body 21.589s
pbkdf2_sha256_sse 0.287s
cfg_get_section 0.062s
SHA256_Final 0.012s
SHA256_Update 0.008s
This time intrinsics aren't counted as function calls. However, the self-test results of the gcc build and icc build show no big difference. This really confuses me.
Lei
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