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[Xen-users] One question about vcpu-wake up in credit scheduler

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] One question about vcpu-wake up in credit scheduler
From: you_bear zhou <youbear.zhou@xxxxxxxxx>
Date: Mon, 11 May 2009 13:09:49 -0400
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Hei guys,

I'm now trying to do an attacking to credit scheduler ( Xen 3.2.0).

As far as I know, the credit scheduler ticks the current runnable vcpu
each 10ms, and a vcpu can wake up with BOOST priority if it was in
UNDER state before waking up.

What I'm trying to do is modifying the cpu_idle loop in linux kernel,
let the idle process first spins for 9ms and then invokes halt(). I
expect the vcpu be blocked right before the tick bound and wakes up
right after that, so it can keep using CPU without paying credits.

However, I found the vcpu seldom woke up. Then I look into the
cpu_idle(), it checks if the cpu needs to reschedule, if so, then
stops the idle loop.

when I change the spin interval to 25ms, it did wake up frequently. So
I think the interrupts should come from the scheduler.

But why the vcpu didn't wake up with 9ms spin interval??

Can anyone explain this to me ?


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