Messages in this thread | | | Date | Mon, 21 Jun 2021 18:57:58 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 5.10 095/146] sched/fair: Correctly insert cfs_rqs to list on unthrottle |
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On Mon, Jun 21, 2021 at 06:15:25PM +0200, Greg Kroah-Hartman wrote: > From: Odin Ugedal <odin@uged.al> > > [ Upstream commit a7b359fc6a37faaf472125867c8dc5a068c90982 ] > > Fix an issue where fairness is decreased since cfs_rq's can end up not > being decayed properly. For two sibling control groups with the same > priority, this can often lead to a load ratio of 99/1 (!!). > > This happens because when a cfs_rq is throttled, all the descendant > cfs_rq's will be removed from the leaf list. When they initial cfs_rq > is unthrottled, it will currently only re add descendant cfs_rq's if > they have one or more entities enqueued. This is not a perfect > heuristic. > > Instead, we insert all cfs_rq's that contain one or more enqueued > entities, or it its load is not completely decayed. > > Can often lead to situations like this for equally weighted control > groups: > > $ ps u -C stress > USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND > root 10009 88.8 0.0 3676 100 pts/1 R+ 11:04 0:13 stress --cpu 1 > root 10023 3.0 0.0 3676 104 pts/1 R+ 11:04 0:00 stress --cpu 1 > > Fixes: 31bc6aeaab1d ("sched/fair: Optimize update_blocked_averages()") > [vingo: !SMP build fix] > Signed-off-by: Odin Ugedal <odin@uged.al> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> > Link: https://lore.kernel.org/r/20210612112815.61678-1-odin@uged.al > Signed-off-by: Sasha Levin <sashal@kernel.org>
This one is currently known to cause some LTP fail, fixes are being discussed, please hold off for now.
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