Messages in this thread | | | Date | Wed, 10 Feb 2016 21:31:05 +0800 | From | Fengguang Wu <> | Subject | Re: [PATCH] Optimize int_sqrt for small values for faster idle |
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On Tue, Feb 09, 2016 at 12:44:00PM -0800, Andi Kleen wrote: > On Sun, Feb 07, 2016 at 10:32:26PM +0100, Rasmus Villemoes wrote: > > On Mon, Feb 01 2016, Andi Kleen <ak@linux.intel.com> wrote: > > > > > On Mon, Feb 01, 2016 at 10:25:17PM +0100, Rasmus Villemoes wrote: > > >> On Thu, Jan 28 2016, Andi Kleen <andi@firstfloor.org> wrote: > > >> > > >> > From: Andi Kleen <ak@linux.intel.com> > > >> > > > >> > The menu cpuidle governor does at least two int_sqrt() each time > > >> > we go into idle in get_typical_interval to compute stddev > > >> > > > >> > int_sqrts take 100-120 cycles each. Short idle latency is important > > >> > for many workloads. > > >> > > > >> > > >> If you want to optimize get_typical_interval(), why not just take the > > >> square root out of the equation (literally)? > > >> > > >> Something like > > > > > > Looks good. Yes that's a better fix. > > > > > > > Andi, did you have a way to measure the impact, and if so, could I get > > you to run the numbers again with my patch? > > I got the numbers from the 0day runs (AIM7 gets faster) > In theory if you post the patch that should happen automatically > (checking with Fengguang)
Yes we bisect and report a lot of runtime performance changes. On the other hand, some few will be missed, too, due to various unstableness issues. Anyway if you would like to study performance impacts of a patch, feel free to send us requests to gather the numbers and do comparison.
Thanks, Fengguang
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