linux-kernel - Re: [PATCH 0/7] KVM: Suspend and cpu hotplug fixes

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Message-ID: <46595B7F.9030006@qumranet.com>
Date:	Sun, 27 May 2007 13:20:47 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Shaohua Li <shaohua.li@...el.com>
CC:	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	lhcs-devel@...ts.sourceforge.net
Subject: Re: [PATCH 0/7] KVM: Suspend and cpu hotplug fixes

Avi Kivity wrote:
> I estimate that that take_cpu_down will run for about a millisecond if
> there are a few hundred vcpus which have last run on the dying cpu (and
> that's an extreme case, which is not expected in normal operation).

I measured vmclear time on an uncached vmcs (which would be all except 
for a handful which are cached on the cpu core) at 144 cycles.  Assuming 
a couple of cache misses for walking the list and accessing the vmcs, 
we're at about 500 cycles per vcpu, or 250us @ 2GHz.  So worst case is 
significantly less than 1 ms.

Is this acceptable for take_cpu_down()?

-- 
error compiling committee.c: too many arguments to function

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