• Hailong Liu's avatar
    sched/rt: Restore rt_runtime after disabling RT_RUNTIME_SHARE · d35aab9d
    Hailong Liu authored
    [ Upstream commit f3d133ee ]
    
    NO_RT_RUNTIME_SHARE feature is used to prevent a CPU borrow enough
    runtime with a spin-rt-task.
    
    However, if RT_RUNTIME_SHARE feature is enabled and rt_rq has borrowd
    enough rt_runtime at the beginning, rt_runtime can't be restored to
    its initial bandwidth rt_runtime after we disable RT_RUNTIME_SHARE.
    
    E.g. on my PC with 4 cores, procedure to reproduce:
    1) Make sure  RT_RUNTIME_SHARE is enabled
     cat /sys/kernel/debug/sched_features
      GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY
      CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_DOUBLE_TICK
      LB_BIAS NONTASK_CAPACITY TTWU_QUEUE NO_SIS_AVG_CPU SIS_PROP
      NO_WARN_DOUBLE_CLOCK RT_PUSH_IPI RT_RUNTIME_SHARE NO_LB_MIN
      ATTACH_AGE_LOAD WA_IDLE WA_WEIGHT WA_BIAS
    2) Start a spin-rt-task
     ./loop_rr &
    3) set affinity to the last cpu
     taskset -p 8 $pid_of_loop_rr
    4) Observe that last cpu have borrowed enough runtime.
     cat /proc/sched_debug | grep rt_runtime
      .rt_runtime                    : 950.000000
      .rt_runtime                    : 900.000000
      .rt_runtime                    : 950.000000
      .rt_runtime                    : 1000.000000
    5) Disable RT_RUNTIME_SHARE
     echo NO_RT_RUNTIME_SHARE > /sys/kernel/debug/sched_features
    6) Observe that rt_runtime can not been restored
     cat /proc/sched_debug | grep rt_runtime
      .rt_runtime                    : 950.000000
      .rt_runtime                    : 900.000000
      .rt_runtime                    : 950.000000
      .rt_runtime                    : 1000.000000
    
    This patch help to restore rt_runtime after we disable
    RT_RUNTIME_SHARE.
    Signed-off-by: default avatarHailong Liu <liu.hailong6@zte.com.cn>
    Signed-off-by: default avatarJiang Biao <jiang.biao2@zte.com.cn>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: zhong.weidong@zte.com.cn
    Link: http://lkml.kernel.org/r/1531874815-39357-1-git-send-email-liu.hailong6@zte.com.cnSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    Signed-off-by: default avatarSasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    d35aab9d