linux-kernel - Re: [PATCH] posix-timers: RCU conversion

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Date:	Tue, 5 Apr 2011 15:35:40 +0545
From:	Ben Nagy <ben@...u.net>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Avi Kivity <avi@...hat.com>, Eric Dumazet <eric.dumazet@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	KVM list <kvm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	John Stultz <johnstul@...ibm.com>,
	Richard Cochran <richard.cochran@...cron.at>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH] posix-timers: RCU conversion

On Tue, Apr 5, 2011 at 2:48 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Tue, 2011-04-05 at 11:56 +0300, Avi Kivity wrote:
>>
>> Could be waking up due to guest wakeups, or qemu internal wakeups
>> (display refresh) or due to guest timer sources which are masked away in
>> the guest (if that's the case we should optimize it away).
>
> Right, so I guess we're all clutching at straws here :-)
>
> Ben how usable is that system when its in that state? Could you run a
> function trace or a trace with all kvm and sched trace-events enabled?

I'm just rebuilding the storage on the network to work around an ocfs2
kernel oops (trying nfs/rdma) so I can't test anything just at the
moment.

I ran some tests under load with the local ext4 ssd, and, weirdly,
everything looked to be just fine - the huge bulk of the system time
was in svm_vcpu_run, which is as it should be I guess, but that was
with only 60 loaded guests.

I'll be able to repeat the same workload test tomorrow, and I'll see
how the perf top stuff looks. I should also be able to repeat the '96
idle guests' test and see if it's the same - if so we'll do that
tracing. My kernel's a moving target at the moment, sorry, we're
tracking the natty git (with Eric's rcu patch merged in).

Thanks, all,

ben
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