On Tue, Mar 18, 2014 at 07:14:04PM -0700, Jason Low wrote: > On Tue, Mar 18, 2014 at 2:16 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Mon, Mar 17, 2014 at 05:20:10PM -0700, Davidlohr Bueso wrote: > >> On Thu, 2013-12-19 at 11:51 -0800, tip-bot for Len Brown wrote: > >> > Commit-ID: 40e2d7f9b5dae048789c64672bf3027fbb663ffa > >> > Gitweb: http://git.kernel.org/tip/40e2d7f9b5dae048789c64672bf3027fbb663ffa > >> > Author: Len Brown <len.brown@xxxxxxxxx> > >> > AuthorDate: Wed, 18 Dec 2013 16:44:57 -0500 > >> > Committer: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx> > >> > CommitDate: Thu, 19 Dec 2013 11:47:39 -0800 > >> > > >> > x86 idle: Repair large-server 50-watt idle-power regression > >> > >> FYI this commit can cause some non trivial performance regressions for > >> larger core count systems. While not surprising because of the nature of > >> the change, having intel_idle do more cacheline invalidations, I still > >> wanted to let you guys know. For instance, on a 160 core Westmere > >> system, aim7 throughput can go down in a number of tests, anywhere from > >> -10% to -25%. > >> > >> I guess it comes down to one of those performance vs energy things. And > >> sure, max_cstate can be set to overcome this, but it's still something > >> that was previously taken for granted. > > > > -10% to -25% seems a lot for a single cacheline flush. Also I would > > expect the expected idle time to be very short while running aim7. So > > could it be the cacheflush is actually taking longer than the expected > > idle time? > > Can we consider conditionally skipping the cacheline flush if the > approximate average CPU idle time is very short, for instance, > something along the lines of skipping if CPU average idle time < > (sched migration cost or "cacheline_flush_penalty")? I'd say its too early for proposing solutions; first we need to find facts about what is happening. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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