On Mon, Jun 21, 2021 at 06:57:58PM +0200, Peter Zijlstra wrote:
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.
Now dropped from all queues, thanks.
greg k-h