linux-kernel - Re: [RFC PATCH 0/3] directed yield for Pause Loop Exiting

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Message-ID: <4D0328CC.1020809@redhat.com>
Date:	Sat, 11 Dec 2010 09:31:24 +0200
From:	Avi Kivity <avi@...hat.com>
To:	balbir@...ux.vnet.ibm.com
CC:	Rik van Riel <riel@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Anthony Liguori <aliguori@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 0/3] directed yield for Pause Loop Exiting

On 12/10/2010 07:03 AM, Balbir Singh wrote:
> >
> >  Scheduler people, please flame me with anything I may have done
> >  wrong, so I can do it right for a next version :)
> >
>
> This is a good problem statement, there are other things to consider
> as well
>
> 1. If a hard limit feature is enabled underneath, donating the
> timeslice would probably not make too much sense in that case

What's the alternative?

Consider a two vcpu guest with a 50% hard cap.  Suppose the workload 
involves ping-ponging within the guest.  If the scheduler decides to 
schedule the vcpus without any overlap, then the throughput will be 
dictated by the time slice.  If we allow donation, throughput is limited 
by context switch latency.


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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