From: Fam Zheng <famz@redhat.com>
To: Ed Swierk <eswierk@skyportsystems.com>
Cc: qemu-devel@nongnu.org, stefanha@redhat.com
Subject: Re: [Qemu-devel] virtio-scsi-pci iothread spins at 100%
Date: Thu, 9 Feb 2017 09:47:28 +0800 [thread overview]
Message-ID: <20170209014728.GF22807@lemon.lan> (raw)
In-Reply-To: <CAO_EM_m9Z7WcxRZthAGgeDgJ6UuwKXwAOEH7NC2=hL8Cd4jABg@mail.gmail.com>
On Wed, 02/08 08:33, Ed Swierk wrote:
> Recently I noticed that when I configure a virtio-scsi-pci device
> using an iothread, as soon as the guest virtio-scsi driver loads, the
> iothread spins at 100%:
>
> -object iothread,id=iothread1 -device virtio-scsi-pci,iothread=iothread1
>
> This occurs whether or not a disk is attached, with either
> poll-max-ns=0 or poll-max-ns=32768, and with Linux 3.13, 4.1 and 4.4
> guests. The iothread stops spinning as soon as the guest driver is
> unloaded.
>
> I bisected the issue to commit 684e508c23d28af8d6ed2c62738a0f60447c8274:
>
> aio: add .io_poll_begin/end() callbacks
>
> It doesn't seem to affect performance, but obviously consuming CPU
> cycles when there's no disk attached is undesirable. Is this an
> expected side effect of implementing iothread polling?
No, something is wrong. The polling shouldn't keep running when there is no I/O
activity.
Can you try "perf top" to see what poll handlers are spinning?
Fam
next prev parent reply other threads:[~2017-02-09 1:47 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-08 16:33 [Qemu-devel] virtio-scsi-pci iothread spins at 100% Ed Swierk
2017-02-08 16:54 ` Ed Swierk
2017-02-09 1:47 ` Fam Zheng [this message]
2017-02-09 2:11 ` Ed Swierk
2017-02-09 2:52 ` Fam Zheng
2017-02-09 3:44 ` Ed Swierk
2017-02-09 5:39 ` Fam Zheng
2017-02-09 6:43 ` Fam Zheng
2017-02-09 10:12 ` Fam Zheng
2017-02-09 13:52 ` Ed Swierk
2017-02-09 14:16 ` Fam Zheng
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