• Kan Liang's avatar
    perf stat: Reduce min --interval-print to 10ms · 19afd104
    Kan Liang authored
    The --interval-print parameter was limited to 100ms. However, for
    example, 10ms is required to do sophisticated bandwidth analysis using
    uncore events.
    
    The test shows that the overhead of the system-wide uncore monitoring
    with 10ms interval is only ~2%. So this patch reduces the minimal
    interval-print allowd to 10ms.
    
    But 10ms may not work well for all cases. For example, when the
    cpus/threads number is very large, for system-wide core event monitoring
    the overhead could be high.
    
    To handle this issue, a warning will be displayed when the
    interval-print is set between 10ms to 100ms. So users can make a
    decision according to their specific cases.
    
     # perf stat -e uncore_imc_1/cas_count_read/ -a --interval-print 10 -- sleep 1
    
     print interval < 100ms. The overhead percentage could be high in some
     cases. Please proceed with caution.
     #           time             counts unit events
          0.010200451               0.10 MiB  uncore_imc_1/cas_count_read/
          0.020475117               0.02 MiB  uncore_imc_1/cas_count_read/
          0.030692800               0.01 MiB  uncore_imc_1/cas_count_read/
          0.040948161               0.02 MiB  uncore_imc_1/cas_count_read/
          0.051159564               0.00 MiB  uncore_imc_1/cas_count_read/
    Signed-off-by: default avatarKan Liang <kan.liang@intel.com>
    Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Link: http://lkml.kernel.org/r/1443776674-42511-1-git-send-email-kan.liang@intel.com
    [ Added warning about overhead when using sub 100ms intervals to the man page ]
    Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    19afd104
perf-stat.txt 5.57 KB