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Re: [Qemu-block] QEMU 1.1.2: block IO throttle might occasionally freeze
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-block] QEMU 1.1.2: block IO throttle might occasionally freeze running process's IO to zero |
Date: |
Thu, 1 Dec 2016 11:16:28 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 |
On 01/12/2016 05:07, Bob Chen wrote:
> Test case:
>
> 1. QEMU 1.1.2
> 2. Run fio inside the vm, give it some pressure. Watch the realtime
> throughput
> 3. block_set_io_throttle drive_2 100000000 0 0 2000 0 0 #
> throttle bps and iops, any value
> 4. Observed that the IO is very likely to freeze to zero. The fio
> process stuck!
> 5. Kill the former fio process, start a new one. The IO turns back to normal
>
> Didn't reproduce it with QEMU 2.5.
>
>
> Actually I'm not wishfully thinking the community would help fix this
> bug on such an ancient version. Just hope someone can tell me what is
> the root cause. Then I have to evaluate whether I should move to higher
> version QEMU, or fix this bug on 1.1.2 in-place(if it is a small one).
Hi,
throttling has been rewritten in QEMU 2.0 (see the commits around
5ddfffb, "throttle: Add a new throttling API implementing continuous
leaky bucket.", 2013-09-06), so the root cause is simply that the old
algorithms were buggy. :)
I think that the new implementation has been backported to QEMU versions
as old as 1.1.2, but if you can move to a newer version it would be simpler.
Paolo
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Paolo Bonzini <=