* [Qemu-devel] QEMU 1.1.2: block IO throttle might occasionally freeze running process's IO to zero
@ 2016-12-01 4:07 Bob Chen
2016-12-01 9:52 ` Fam Zheng
2016-12-01 10:16 ` Paolo Bonzini
0 siblings, 2 replies; 3+ messages in thread
From: Bob Chen @ 2016-12-01 4:07 UTC (permalink / raw)
To: qemu-block, qemu-devel
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).
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] QEMU 1.1.2: block IO throttle might occasionally freeze running process's IO to zero
2016-12-01 4:07 [Qemu-devel] QEMU 1.1.2: block IO throttle might occasionally freeze running process's IO to zero Bob Chen
@ 2016-12-01 9:52 ` Fam Zheng
2016-12-01 10:16 ` Paolo Bonzini
1 sibling, 0 replies; 3+ messages in thread
From: Fam Zheng @ 2016-12-01 9:52 UTC (permalink / raw)
To: Bob Chen; +Cc: qemu-block, qemu-devel
On Thu, 12/01 12:07, 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).
The throttling implementation is completely refreshed so I think it's not easy
to suggest a root cause for you.
Fam
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] QEMU 1.1.2: block IO throttle might occasionally freeze running process's IO to zero
2016-12-01 4:07 [Qemu-devel] QEMU 1.1.2: block IO throttle might occasionally freeze running process's IO to zero Bob Chen
2016-12-01 9:52 ` Fam Zheng
@ 2016-12-01 10:16 ` Paolo Bonzini
1 sibling, 0 replies; 3+ messages in thread
From: Paolo Bonzini @ 2016-12-01 10:16 UTC (permalink / raw)
To: Bob Chen, qemu-devel, qemu block
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
^ permalink raw reply [flat|nested] 3+ messages in thread
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2016-12-01 4:07 [Qemu-devel] QEMU 1.1.2: block IO throttle might occasionally freeze running process's IO to zero Bob Chen
2016-12-01 9:52 ` Fam Zheng
2016-12-01 10:16 ` Paolo Bonzini
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