Messages in this thread |  | | Date | Thu, 28 Nov 2013 18:40:01 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 7/8] sched, net: Fixup busy_loop_us_clock() |
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On Thu, Nov 28, 2013 at 06:49:00PM +0200, Eliezer Tamir wrote: > I have tested this patch and I see a performance regression of about > 1.5%.
Cute, can you qualify your metric? Since this is a poll loop the only metric that would be interesting is the response latency. Is that what's increased by 1.5%? Also, what's the standard deviation of your result?
Also, can you provide relevant perf results for this? Is it really the sti;cli pair that's degrading your latency?
Better yet, can you provide us with a simple test-case that we can run locally (preferably single machine setup, using localnet or somesuch).
> Maybe it would be better, rather then testing in the fast path, to > simply disallow busy polling altogether when sched_clock_stable is > not true?
Sadly that doesn't work; sched_clock_stable can become false at any time after boot (and does, even on recent machines).
That said; let me see if I can come up with a few patches to optimize the entire thing; that'd be something we all benefit from.
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