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@xxxxxxx>
> >
> > [ 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@xxxxxxx>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20210612112815.61678-1-odin@xxxxxxx
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
>
> 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
