Re: [RFC PATCH 0/4] Gang scheduling in CFS
From: Nikunj A Dadhania
Date: Mon Dec 26 2011 - 22:19:40 EST
On Mon, 26 Dec 2011 08:44:58 +0530, Nikunj A Dadhania <nikunj@xxxxxxxxxxxxxxxxxx> wrote:
> On Sun, 25 Dec 2011 12:58:15 +0200, Avi Kivity <avi@xxxxxxxxxx> wrote:
> > On 12/23/2011 12:36 PM, Ingo Molnar wrote:
> > > * Nikunj A Dadhania <nikunj@xxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > >
> > > > I see the main difference between both the reports is:
> > > > native_flush_tlb_others.
> > >
> > > So it would be important to figure out why ebizzy gets into so
> > > many TLB flushes and why gang scheduling makes it go away.
> > The second part is easy - a remote tlb flush involves IPIs to many other
> > vcpus (possible waking them up and scheduling them), then busy-waiting
> > until they acknowledge the flush. Gang scheduling is really good here
> > since it shortens the busy wait, would be even better if we schedule
> > halted vcpus (see the yield_on_hlt module parameter, set to 0).
> I will check this.
I am seeing a drop of ~44% when setting yield_on_hlt = 0
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