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Re: [Xen-devel] [PATCH] only set scheduler timer for non-idle CPU

To: Thomas Pfeuffer <thomas.pfeuffer@xxxxxxxx>, "Yu, Ke" <ke.yu@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] only set scheduler timer for non-idle CPU
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 02 Apr 2009 14:06:27 +0100
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On 02/04/2009 13:48, "Thomas Pfeuffer" <thomas.pfeuffer@xxxxxxxx> wrote:

Hello Ke,

It is not necessary to set scheduler timer for idle CPU. so this patch add conditional check for idle CPU.
I think your patch is not good in case sedf-scheduler is used. If idle VCPU is the current "running" VCPU, the scheduler timer is set to the next "period begin" of the first VCPU in the wait queue.
Your patch prevents sedf from taking the VCPUs waiting for their next period into the runnable queue again.

It’s probably cleaner always to respect the specific scheduler’s scheduling quantum in schedule.c, but then have sched_credit.c return a very large quantum (large as possible) for the idle VCPU.

 -- Keir
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