From: Kevin Wolf <kwolf@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: "Zhi Yong Wu" <wuzhy@cn.ibm.com>,
qemu-devel@nongnu.org, "Benoît Canet" <benoit@irqsave.net>
Subject: Re: [Qemu-devel] [PATCH v2 0/4] block: fix I/O throttling oscillations
Date: Fri, 5 Apr 2013 14:32:36 +0200 [thread overview]
Message-ID: <20130405123236.GB2351@dhcp-200-207.str.redhat.com> (raw)
In-Reply-To: <1365154342-10513-1-git-send-email-stefanha@redhat.com>
Am 05.04.2013 um 11:32 hat Stefan Hajnoczi geschrieben:
> Benoît Canet <benoit@irqsave.net> reported that QEMU I/O throttling can
> oscillate under continuous I/O. The test case runs 50 threads performing
> random writes and a -drive iops=150 limit is used.
>
> Since QEMU I/O throttling is implemented using 100 millisecond time slices,
> we'd expect 150 +/- 15 IOPS. Anything outside that range indicates a problem
> with the I/O throttling algorithm.
>
> It turned out that even a single thread performing sequential I/O continuously
> is throttled outside the 150 +/- 15 IOPS range. The continous stream of I/O
> slows down as time goes on but resets to 150 IOPS again when interrupted. This
> can be tested with:
>
> $ iostat -d 1 -x /dev/vdb &
> $ dd if=/dev/vdb of=/dev/null bs=4096 iflag=direct
>
> This patches addresses these problems as follows:
>
> 1. Account for I/O requests when they are submitted instead of completed. This
> ensures that we do not exceed the budget for this slice. Exceeding the
> budget leads to fluctuations since we have to make up for this later.
>
> 2. Use constant 100 millisecond slice time. Adjusting the slice time at
> run-time led to oscillations. Since the reason for adjusting slice time is
> not clear, drop this behavior.
>
> I have also included two code clean-up patches.
>
> Tested-By: Benoit Canet <benoit@irqsave.net>
>
> v2:
> * Account slice_submitted after both bps and iops checks pass [kwolf]
Thanks, applied all to the block branch.
Kevin
prev parent reply other threads:[~2013-04-05 12:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-05 9:32 [Qemu-devel] [PATCH v2 0/4] block: fix I/O throttling oscillations Stefan Hajnoczi
2013-04-05 9:32 ` [Qemu-devel] [PATCH v2 1/4] block: fix I/O throttling accounting blind spot Stefan Hajnoczi
2013-04-05 9:32 ` [Qemu-devel] [PATCH v2 2/4] block: keep I/O throttling slice time constant Stefan Hajnoczi
2013-04-05 9:32 ` [Qemu-devel] [PATCH v2 3/4] block: drop duplicated slice extension code Stefan Hajnoczi
2013-04-05 9:32 ` [Qemu-devel] [PATCH v2 4/4] block: clean up I/O throttling wait_time code Stefan Hajnoczi
2013-04-05 12:32 ` Kevin Wolf [this message]
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