Messages in this thread | | | From | Cong Wang <> | Date | Tue, 1 May 2018 11:06:08 -0700 | Subject | Re: [PATCH] sched/fair: make CFS bandwidth slice per cpu group |
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On Tue, May 1, 2018 at 12:11 AM, Peter Zijlstra <peterz@infradead.org> wrote: > On Mon, Apr 30, 2018 at 01:37:16PM -0700, Cong Wang wrote: >> On Mon, Apr 30, 2018 at 12:42 PM, Peter Zijlstra <peterz@infradead.org> wrote: >> > On Mon, Apr 30, 2018 at 12:29:25PM -0700, Cong Wang wrote: >> >> Currently, the sched_cfs_bandwidth_slice_us is a global setting which >> >> affects all cgroups. Different groups may want different values based >> >> on their own workload, one size doesn't fit all. The global pool filled >> >> periodically is per cgroup too, they should have the right to distribute >> >> their own quota to each local CPU with their own frequency. >> > >> > Why.. what happens? This doesn't really tell us anything. >> >> We saw tasks in a container got throttled for many times even >> when they don't apparently over-burn the CPU's. I tried to reduce >> the sched_cfs_bandwidth_slice_us from the default 5ms to 1ms, >> it solved the problem as no tasks got throttled after this change. >> This is why I want to change it. > > The 1ms slice distributes time better at the cost of higher overhead, > right?
Right, slightly higher. According to this paper [1]:
"While decreasing this value increases the frequency at which CPUs request for quota from the global pool, we did not notice any measurable impact on performance."
1. https://landley.net/kdocs/ols/2010/ols2010-pages-245-254.pdf
> >> And I don't think 1ms will be good for all containers, so in order to >> minimize the impact, I would like to keep the slice change within >> each container. This is why I propose this patch rather just >> `sysctl -w`. Do you think otherwise? > > Well, I think I don't quite remember everything and a Changelog that > tells me why you want stuff in a little more detail and helps me > remember some things is a lot more useful than me having to go dig > through the code myself (which I'll invariably postpone because I'm a > busy sort of person).
Sure, you just tell me how I should improve my changelog. I didn't realize I need to state why I need to change sched_cfs_bandwidth_slice_us since it is already a tunable. I will add it in v2.
> >> BTW, people reported a similar (if not same) issue here before: >> https://gist.github.com/bobrik/2030ff040fad360327a5fab7a09c4ff1 > > That's not a report, that's a random person on the interweb posting > random crap. A report lands in my inbox.
Well, I found it via LKML: https://marc.info/?l=linux-kernel&m=151270583632566&w=2
(I was too lazy to search for the original LKML link.)
I will update this patch to improve the changelog and address kbuild warnings, if you don't object.
Thanks.
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