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    sched/fair: Fix FTQ noise bench regression · bc427898
    Vincent Guittot 提交于
    A regression of the FTQ noise has been reported by Ying Huang,
    on the following hardware:
    
      8 threads Intel(R) Core(TM)i7-4770 CPU @ 3.40GHz with 8G memory
    
    ... which was caused by this commit:
    
      commit 4e516076 ("sched/fair: Propagate asynchrous detach")
    
    The only part of the patch that can increase the noise is the update
    of blocked load of group entity in update_blocked_averages().
    
    We can optimize this call and skip the update of group entity if its load
    and utilization are already null and there is no pending propagation of load
    in the task group.
    
    This optimization partly restores the noise score. A more agressive
    optimization has been tried but has shown worse score.
    
    Reported-by: ying.huang@linux.intel.com
    Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
    Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Mike Galbraith <efault@gmx.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: dietmar.eggemann@arm.com
    Cc: ying.huang@intel.com
    Fixes: 4e516076 ("sched/fair: Propagate asynchrous detach")
    Link: http://lkml.kernel.org/r/1489758442-2877-1-git-send-email-vincent.guittot@linaro.org
    [ Fixed typos, improved layout. ]
    Signed-off-by: NIngo Molnar <mingo@kernel.org>
    bc427898
fair.c 249.2 KB