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Re: [PATCH v7 0/3] support dirty restraint on vCPU

From: Peter Xu
Subject: Re: [PATCH v7 0/3] support dirty restraint on vCPU
Date: Tue, 30 Nov 2021 20:57:47 +0800

On Tue, Nov 30, 2021 at 06:28:10PM +0800, huangy81@chinatelecom.cn wrote:
> From: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
> The patch [2/3] has not been touched so far. Any corrections and
> suggetions are welcome. 

I played with it today, but the vcpu didn't got throttled as expected.

What I did was starting two workload with 500mb/s, each pinned on one vcpu

[root@fedora ~]# pgrep -fa mig_mon
595 ./mig_mon mm_dirty 1000 500 sequential
604 ./mig_mon mm_dirty 1000 500 sequential
[root@fedora ~]# taskset -pc 595
pid 595's current affinity list: 2
[root@fedora ~]# taskset -pc 604
pid 604's current affinity list: 3

Then start throttle with 100mb/s:

(QEMU) set-dirty-limit cpu-index=3 dirty-rate=100
{"return": {}}
(QEMU) set-dirty-limit cpu-index=2 dirty-rate=100
{"return": {}}

I can see the workload dropped a tiny little bit (perhaps 500mb -> 499mb), then
it keeps going..

Further throttle won't work too:

(QEMU) set-dirty-limit cpu-index=2 dirty-rate=10
{"return": {}}

Funnily, the ssh client got slowed down instead... :(

Yong, how did you test it?

Peter Xu

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