From: Paolo Bonzini <pbonzini@redhat.com>
To: Anthony Liguori <aliguori@us.ibm.com>,
qemu-devel <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH] main-loop: drop the BQL if the I/O appears to be spinning
Date: Fri, 05 Apr 2013 17:05:10 +0200 [thread overview]
Message-ID: <515EE826.2040201@redhat.com> (raw)
In-Reply-To: <1365169560-11012-1-git-send-email-aliguori@us.ibm.com>
Il 05/04/2013 15:46, Anthony Liguori ha scritto:
> The char-flow refactoring introduced a busy-wait that depended on
> an action from the VCPU thread. However, the VCPU thread could
> never take that action because the busy-wait starved the VCPU thread
> of the BQL because it never dropped the mutex while running select.
>
> Paolo doesn't want to drop this optimization for fear that we will
> stop detecting these busy waits. I'm afraid to keep this optimization
> even with the busy-wait fixed because I think a similar problem can
> occur just with heavy I/O thread load manifesting itself as VCPU pauses.
>
> As a compromise, introduce an artificial timeout after a thousand
> iterations but print a rate limited warning when this happens. This
> let's us still detect when this condition occurs without it being
> a fatal error.
Good idea, thanks!
Paolo
next prev parent reply other threads:[~2013-04-05 15:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-05 13:46 [Qemu-devel] [PATCH] main-loop: drop the BQL if the I/O appears to be spinning Anthony Liguori
2013-04-05 15:04 ` Eric Blake
2013-04-05 15:45 ` Anthony Liguori
2013-04-05 15:05 ` Paolo Bonzini [this message]
2013-04-07 5:12 ` Peter Crosthwaite
2013-04-08 21:55 ` Anthony Liguori
2013-04-09 17:50 ` Andreas Färber
2013-04-09 18:28 ` Anthony Liguori
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