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From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <1495229390-18909-1-git-send-email-felipe@nutanix.com> (Felipe
	Franciosi's message of "Fri, 19 May 2017 22:29:50 +0100")
References: <1495229390-18909-1-git-send-email-felipe@nutanix.com>
Reply-To: quintela@redhat.com
Date: Wed, 07 Jun 2017 18:26:39 +0200
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Subject: Re: [Qemu-devel] [PATCH] cpus: reset throttle_thread_scheduled
 after sleep
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To: Felipe Franciosi <felipe@nutanix.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, "Jason J. Herne" <jjherne@linux.vnet.ibm.com>, Malcolm Crossley <malcolm@nutanix.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

Felipe Franciosi <felipe@nutanix.com> wrote:
> Currently, the throttle_thread_scheduled flag is reset back to 0 before
> sleeping (as part of the throttling logic). Given that throttle_timer
> (well, any timer) may tick with a slight delay, it so happens that under
> heavy throttling (ie. close or on CPU_THROTTLE_PCT_MAX) the tick may
> schedule a further cpu_throttle_thread() work item after the flag reset,
> but before the previous sleep completed. This results on the vCPU thread
> sleeping continuously for potentially several seconds in a row.
>
> The chances of that happening can be drastically minimised by resetting
> the flag after the sleep.
>
> Signed-off-by: Felipe Franciosi <felipe@nutanix.com>
> Signed-off-by: Malcolm Crossley <malcolm@nutanix.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>

Paolo, I think that the analisys makes sense.

Should you pull this patch, or do you want me to pull it?

Thanks, Juan.