linux-kernel - Re: [RFC -v3 PATCH 2/3] sched: add yield

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Message-ID: <4D2350AE.60302@redhat.com>
Date:	Tue, 04 Jan 2011 11:54:06 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Hillf Danton <dhillf@...il.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Avi Kiviti <avi@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function

On 01/04/2011 11:51 AM, Hillf Danton wrote:

>> Wouldn't that break for FIFO and RR tasks?
>>
>> There's a reason all the scheduler folks wanted a
>> per-class yield_to_task function :)
>>
>
> Where is the yield_to callback in the patch for RT schedule class?
> If @p is RT, what could you do?

If the user chooses to overcommit the CPU with realtime
tasks, the user cannot expect realtime response.

For realtime, I have not implemented the yield_to callback
at all because it would probably break realtime semantics
and I assume people will not overcommit the CPU with realtime
tasks anyway.

I could see running a few realtime guests on a system, with
the number of realtime VCPUs not exceeding the number of
physical CPUs.

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