Messages in this thread | | | Date | Sat, 21 Feb 2015 19:39:52 +0100 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs |
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* Borislav Petkov <bp@alien8.de> wrote:
> On Sat, Feb 21, 2015 at 05:38:40PM +0100, Borislav Petkov wrote: > > My assumption is that libc uses SSE for memcpy and thus the FPU will > > be used. (I'll trace FPU-specific PMCs later to confirm). > > Ok, so I slapped a trace_printk() at the beginning of fpu_save_init() > and did a kernel build once with default 3.19 and once with Andy's > patch. So we end up with this count: > > default: 712000 > eager: 780000 > > This would explain the very small difference in the > performance counters data from the previous email.
So the workload improved by ~600,000 usecs, and there's 68,000 less calls, so it saved 8.8 usecs per call. Isn't that a bit too high?
I'd sleep a lot better if we had some runtime debug flag to be able to do run-to-run comparisons on the same booted up kernel, or so.
Thanks,
Ingo
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