• Jiri Olsa's avatar
    x86: Separate out entry text section · ea714547
    Jiri Olsa authored
    Put x86 entry code into a separate link section: .entry.text.
    
    Separating the entry text section seems to have performance
    benefits - caused by more efficient instruction cache usage.
    
    Running hackbench with perf stat --repeat showed that the change
    compresses the icache footprint. The icache load miss rate went
    down by about 15%:
    
     before patch:
             19417627  L1-icache-load-misses      ( +-   0.147% )
    
     after patch:
             16490788  L1-icache-load-misses      ( +-   0.180% )
    
    The motivation of the patch was to fix a particular kprobes
    bug that relates to the entry text section, the performance
    advantage was discovered accidentally.
    
    Whole perf output follows:
    
     - results for current tip tree:
    
      Performance counter stats for './hackbench/hackbench 10' (500 runs):
    
             19417627  L1-icache-load-misses      ( +-   0.147% )
           2676914223  instructions             #      0.497 IPC     ( +- 0.079% )
           5389516026  cycles                     ( +-   0.144% )
    
          0.206267711  seconds time elapsed   ( +-   0.138% )
    
     - results for current tip tree with the patch applied:
    
      Performance counter stats for './hackbench/hackbench 10' (500 runs):
    
             16490788  L1-icache-load-misses      ( +-   0.180% )
           2717734941  instructions             #      0.502 IPC     ( +- 0.079% )
           5414756975  cycles                     ( +-   0.148% )
    
          0.206747566  seconds time elapsed   ( +-   0.137% )
    Signed-off-by: default avatarJiri Olsa <jolsa@redhat.com>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Nick Piggin <npiggin@kernel.dk>
    Cc: Eric Dumazet <eric.dumazet@gmail.com>
    Cc: masami.hiramatsu.pt@hitachi.com
    Cc: ananth@in.ibm.com
    Cc: davem@davemloft.net
    Cc: 2nddept-manager@sdl.hitachi.co.jp
    LKML-Reference: <20110307181039.GB15197@jolsa.redhat.com>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    ea714547
entry_64.S 37.2 KB