lkml.org 
[lkml]   [2021]   [Jun]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 5.10 095/146] sched/fair: Correctly insert cfs_rqs to list on unthrottle
    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.

    \
     
     \ /
      Last update: 2021-06-21 19:07    [W:4.697 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site