1. 09 8月, 2011 1 次提交
  2. 06 8月, 2011 1 次提交
    • J
      jump label: Reduce the cycle count by changing the link order · b77f0f3c
      Jason Baron 提交于
      In the course of testing jump labels for use with the CFS
      bandwidth controller, Paul Turner, discovered that using jump
      labels reduced the branch count and the instruction count, but
      did not reduce the cycle count or wall time.
      
      I noticed that having the jump_label.o included in the kernel
      but not used in any way still caused this increase in cycle
      count and wall time. Thus, I moved jump_label.o in the
      kernel/Makefile, thus changing the link order, and presumably
      moving it out of hot icache areas. This brought down the cycle
      count/time as expected.
      
      In addition to Paul's testing,  I've tested the patch using a
      single 'static_branch()' in the getppid() path, and basically
      running tight loops of calls to getppid(). Here are my results
      for the branch disabled case:
      
      With jump labels turned on (CONFIG_JUMP_LABEL), branch disabled:
      
       Performance counter stats for 'bash -c /tmp/getppid;true' (50 runs):
      
           3,969,510,217 instructions             #	   0.864 IPC     ( +-0.000% )
           4,592,334,954 cycles                     ( +-   0.046% )
             751,634,470 branches                   ( +-   0.000% )
      
              1.722635797  seconds time elapsed   ( +-   0.046% )
      
      Jump labels turned off (CONFIG_JUMP_LABEL not set), branch
      disabled:
      
       Performance counter stats for 'bash -c /tmp/getppid;true' (50 runs):
      
           4,009,611,846 instructions             #	   0.867 IPC     ( +-0.000% )
           4,622,210,580 cycles                     ( +-   0.012% )
             771,662,904 branches                   ( +-   0.000% )
      
              1.734341454  seconds time elapsed   ( +-   0.022% )
      Signed-off-by: NJason Baron <jbaron@redhat.com>
      Cc: rth@redhat.com
      Cc: a.p.zijlstra@chello.nl
      Cc: rostedt@goodmis.org
      Link: http://lkml.kernel.org/r/20110805204040.GG2522@redhat.comSigned-off-by: NIngo Molnar <mingo@elte.hu>
      Tested-by: NPaul Turner <pjt@google.com>
      b77f0f3c
  3. 05 8月, 2011 13 次提交
  4. 04 8月, 2011 25 次提交