* [Qemu-devel] Confusing I/O throttling behavior with burst_length > 1 and max < avg
@ 2016-07-14 12:18 Stefan Hajnoczi
2016-07-26 12:38 ` Alberto Garcia
0 siblings, 1 reply; 3+ messages in thread
From: Stefan Hajnoczi @ 2016-07-14 12:18 UTC (permalink / raw)
To: qemu-devel; +Cc: Alberto Garcia, ngu
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Hi Berto,
The following throttling behavior was observed with bps=512000
bps_max=51200 throttling.bps-total-max-length=2:
READ: io=512KB, aggrb=50KB/s, minb=50KB/s, maxb=50KB/s, mint=10061msec, maxt=10061msec
If bps-total-max-length=1 then the result is different:
READ: io=5056KB, aggrb=505KB/s, minb=505KB/s, maxb=505KB/s, mint=10006msec, maxt=10006msec
The burst limits guest bps instead of adding on top of it when
burst_length > 1.
I'm not sure what behavior you intended? Replacing the following should
allow the guest to get its burst on top of the bps:
return throttle_do_compute_wait(bkt->max, extra);
with:
return throttle_do_compute_wait(MAX(bkt->avg, bkt->max), extra);
What do you think?
For more details, see Nini Gu's bug report:
https://bugzilla.redhat.com/show_bug.cgi?id=1355665
Stefan
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] Confusing I/O throttling behavior with burst_length > 1 and max < avg
2016-07-14 12:18 [Qemu-devel] Confusing I/O throttling behavior with burst_length > 1 and max < avg Stefan Hajnoczi
@ 2016-07-26 12:38 ` Alberto Garcia
0 siblings, 0 replies; 3+ messages in thread
From: Alberto Garcia @ 2016-07-26 12:38 UTC (permalink / raw)
To: Stefan Hajnoczi; +Cc: qemu-devel, ngu
On Thu, Jul 14, 2016 at 01:18:19PM +0100, Stefan Hajnoczi wrote:
> The following throttling behavior was observed with bps=512000
> bps_max=51200 throttling.bps-total-max-length=2:
>
> READ: io=512KB, aggrb=50KB/s, minb=50KB/s, maxb=50KB/s, mint=10061msec, maxt=10061msec
>
> If bps-total-max-length=1 then the result is different:
>
> READ: io=5056KB, aggrb=505KB/s, minb=505KB/s, maxb=505KB/s, mint=10006msec, maxt=10006msec
>
> The burst limits guest bps instead of adding on top of it when
> burst_length > 1.
Thanks Stefan,
I think we should forbid that kind of setup altogether. I wrote a few
more details in the bug report:
> https://bugzilla.redhat.com/show_bug.cgi?id=1355665
I can write the patch.
Berto
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Qemu-devel] Confusing I/O throttling behavior with burst_length > 1 and max < avg
@ 2016-07-14 12:18 Stefan Hajnoczi
0 siblings, 0 replies; 3+ messages in thread
From: Stefan Hajnoczi @ 2016-07-14 12:18 UTC (permalink / raw)
To: qemu-devel; +Cc: Alberto Garcia, ngu
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Hi Berto,
The following throttling behavior was observed with bps=512000
bps_max=51200 throttling.bps-total-max-length=2:
READ: io=512KB, aggrb=50KB/s, minb=50KB/s, maxb=50KB/s, mint=10061msec, maxt=10061msec
If bps-total-max-length=1 then the result is different:
READ: io=5056KB, aggrb=505KB/s, minb=505KB/s, maxb=505KB/s, mint=10006msec, maxt=10006msec
The burst limits guest bps instead of adding on top of it when
burst_length > 1.
I'm not sure what behavior you intended? Replacing the following should
allow the guest to get its burst on top of the bps:
return throttle_do_compute_wait(bkt->max, extra);
with:
return throttle_do_compute_wait(MAX(bkt->avg, bkt->max), extra);
What do you think?
For more details, see Nini Gu's bug report:
https://bugzilla.redhat.com/show_bug.cgi?id=1355665
Stefan
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2016-07-26 12:38 ` Alberto Garcia
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