1. 21 Aug, 2009 1 commit
    • Peter Zijlstra's avatar
      timer: delay waking softirqs from the jiffy tick · 3e465345
      Peter Zijlstra authored
      People were complaining about broken balancing with the recent -rt
      series.
      
      A look at /proc/sched_debug yielded:
      
      cpu#0, 2393.874 MHz
        .nr_running                    : 0
        .load                          : 0
        .cpu_load[0]                   : 177522
        .cpu_load[1]                   : 177522
        .cpu_load[2]                   : 177522
        .cpu_load[3]                   : 177522
        .cpu_load[4]                   : 177522
      cpu#1, 2393.874 MHz
        .nr_running                    : 4
        .load                          : 4096
        .cpu_load[0]                   : 181618
        .cpu_load[1]                   : 180850
        .cpu_load[2]                   : 180274
        .cpu_load[3]                   : 179938
        .cpu_load[4]                   : 179758
      
      Which indicated the cpu_load computation was hosed, the 177522 value
      indicates that there is one RT task runnable. Initially I thought the
      old problem of calculating the cpu_load from a softirq had re-surfaced,
      however looking at the code shows its being done from scheduler_tick().
      
      [ we really should fix this RT/cfs interaction some day... ]
      
      A few trace_printk()s later:
      
          sirq-timer/1-19    [001]   174.289744:     19: 50:S ==> [001]     0:140:R <idle>                            
                <idle>-0     [001]   174.290724: enqueue_task_rt: adding task: 19/sirq-timer/1 with load: 177522      
                <idle>-0     [001]   174.290725:      0:140:R   + [001]    19: 50:S sirq-timer/1                      
                <idle>-0     [001]   174.290730: scheduler_tick: current load: 177522                                 
                <idle>-0     [001]   174.290732: scheduler_tick: current: 0/swapper                                   
                <idle>-0     [001]   174.290736:      0:140:R ==> [001]    19: 50:R sirq-timer/1                      
          sirq-timer/1-19    [001]   174.290741: dequeue_task_rt: removing task: 19/sirq-timer/1 with load: 177522    
          sirq-timer/1-19    [001]   174.290743:     19: 50:S ==> [001]     0:140:R <idle>  
      
      We see that we always raise the timer softirq before doing the load
      calculation. Avoid this by re-ordering the scheduler_tick() call in
      update_process_times() to occur before we deal with timers.
      
      This lowers the load back to sanity and restores regular load-balancing
      behaviour.
      Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      3e465345
  2. 19 Aug, 2009 8 commits
  3. 18 Aug, 2009 23 commits
  4. 17 Aug, 2009 8 commits