linux-kernel - Re: [RFC PATCH 0/4] Gang scheduling in CFS

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Message-ID: <877gzhpvpv.fsf@abhimanyu.in.ibm.com>
Date:	Mon, 20 Feb 2012 17:23:16 +0530
From:	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>, Avi Kivity <avi@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Rik van Riel <riel@...hat.com>,
	linux-kernel@...r.kernel.org, vatsa@...ux.vnet.ibm.com,
	bharata@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH 0/4] Gang scheduling in CFS

On Mon, 20 Feb 2012 11:51:13 +0100, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, 2012-02-20 at 13:38 +0530, Nikunj A Dadhania wrote:
> > +#ifdef CONFIG_PARAVIRT_FLUSH_TLB
> > +               while (!cpumask_empty(to_cpumask(f->flush_cpumask)) && --loop)
> > +                       cpu_relax();
> > +               if (!loop && !cpumask_empty(to_cpumask(f->flush_cpumask)))
> > +                       halt();
> 
> 
> That's just vile, you don't need to wait for it, all you need to make
> sure is that when that vcpu wakes up it does the flush.
>
Yes, but we are not sure the vcpu will be sleeping or running. In the
case where vcpus are running, it might be beneficial to wait a while.

For example: If its a remote flush to only one of the vcpu and its
already running, is it worthed to halt and come back?

Regards,
Nikunj

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