Messages in this thread | | | Date | Thu, 17 Mar 2022 00:13:11 +0800 | From | Chen Yu <> | Subject | Re: [PATCH v2][RFC] sched/fair: Change SIS_PROP to search idle CPU based on sum of util_avg |
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On Mon, Mar 14, 2022 at 10:34:30AM -0700, Tim Chen wrote: > On Mon, 2022-03-14 at 20:56 +0800, Chen Yu wrote: > > > > > > > > So nr_scan will probably be updated at llc-domain-lb-interval, which > > > is llc_size milliseconds. Since load can be varied a lot during such > > > a period, would this brought accuracy issues? > > > > > I agree there might be delay in reflecting the latest utilization. > > The sum_util calculated by periodic load balance after 112ms would be > > decay to about 0.5 * 0.5 * 0.5 * 0.7 = 8.75%. > > But consider that this is a server platform, I have an impression that > > the CPU utilization jitter during a small period of time is not a regular > > scenario? It seems to be a trade-off. Checking the util_avg in newidle > > load balance path would be more frequent, but it also brings overhead - > > multiple CPUs write/read the per-LLC shared variable and introduces cache > > false sharing. But to make this more robust, maybe we can add time interval > > control in newidle load balance too. > > > > > > Also the idea is we allow ourselves to be non-optimal in terms of > scheduling for the short term variations. But we want to make sure that if > there's a long term trend in the load behavior, the scheduler should > adjust for that. I think if you see high utilization and CPUs are > all close to fully busy for quite a while, that is a long term trend > that overwhelms any short load jitters. > Agree. From long term trend, the scheduler should approach an optimization status.
thanks, Chenyu > Tim >
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