1. 25 Aug, 2008 1 commit
    • Peter Zijlstra's avatar
      sched_clock: fix cpu_clock() · 354879bb
      Peter Zijlstra authored
      This patch fixes 3 issues:
      
      a) it removes the dependency on jiffies, because jiffies are incremented
         by a single CPU, and the tick is not synchronized between CPUs. Therefore
         relying on it to calculate a window to clip whacky TSC values doesn't work
         as it can drift around.
      
         So instead use [GTOD, GTOD+TICK_NSEC) as the window.
      
      b) __update_sched_clock() did (roughly speaking):
      
         delta = sched_clock() - scd->tick_raw;
         clock += delta;
      
         Which gives exponential growth, instead of linear.
      
      c) allows the sched_clock_cpu() value to warp the u64 without breaking.
      
      the results are more reliable sched_clock() deltas:
      
                 before       after   sched_clock
      
      cpu_clock: 15750        51312   51488
      cpu_clock: 59719        51052   50947
      cpu_clock: 15879        51249   51061
      cpu_clock: 1            50933   51198
      cpu_clock: 1            50931   51039
      cpu_clock: 1            51093   50981
      cpu_clock: 1            51043   51040
      cpu_clock: 1            50959   50938
      cpu_clock: 1            50981   51011
      cpu_clock: 1            51364   51212
      cpu_clock: 1            51219   51273
      cpu_clock: 1            51389   51048
      cpu_clock: 1            51285   51611
      cpu_clock: 1            50964   51137
      cpu_clock: 1            50973   50968
      cpu_clock: 1            50967   50972
      cpu_clock: 1            58910   58485
      cpu_clock: 1            51082   51025
      cpu_clock: 1            50957   50958
      cpu_clock: 1            50958   50957
      cpu_clock: 1006128      51128   50971
      cpu_clock: 1            51107   51155
      cpu_clock: 1            51371   51081
      cpu_clock: 1            51104   51365
      cpu_clock: 1            51363   51309
      cpu_clock: 1            51107   51160
      cpu_clock: 1            51139   51100
      cpu_clock: 1            51216   51136
      cpu_clock: 1            51207   51215
      cpu_clock: 1            51087   51263
      cpu_clock: 1            51249   51177
      cpu_clock: 1            51519   51412
      cpu_clock: 1            51416   51255
      cpu_clock: 1            51591   51594
      cpu_clock: 1            50966   51374
      cpu_clock: 1            50966   50966
      cpu_clock: 1            51291   50948
      cpu_clock: 1            50973   50867
      cpu_clock: 1            50970   50970
      cpu_clock: 998306       50970   50971
      cpu_clock: 1            50971   50970
      cpu_clock: 1            50970   50970
      cpu_clock: 1            50971   50971
      cpu_clock: 1            50970   50970
      cpu_clock: 1            51351   50970
      cpu_clock: 1            50970   51352
      cpu_clock: 1            50971   50970
      cpu_clock: 1            50970   50970
      cpu_clock: 1            51321   50971
      cpu_clock: 1            50974   51324
      Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      354879bb
  2. 21 Aug, 2008 1 commit
  3. 19 Aug, 2008 2 commits
  4. 18 Aug, 2008 36 commits