• Dave Hansen's avatar
    perf: Drop sample rate when sampling is too slow · 14c63f17
    Dave Hansen authored
    This patch keeps track of how long perf's NMI handler is taking,
    and also calculates how many samples perf can take a second.  If
    the sample length times the expected max number of samples
    exceeds a configurable threshold, it drops the sample rate.
    This way, we don't have a runaway sampling process eating up the
    This patch can tend to drop the sample rate down to level where
    perf doesn't work very well.  *BUT* the alternative is that my
    system hangs because it spends all of its time handling NMIs.
    I'll take a busted performance tool over an entire system that's
    busted and undebuggable any day.
    BTW, my suspicion is that there's still an underlying bug here.
    Using the HPET instead of the TSC is definitely a contributing
    factor, but I suspect there are some other things going on.
    But, I can't go dig down on a bug like that with my machine
    hanging all the time.
    Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
    Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: paulus@samba.org
    Cc: acme@ghostprotocols.net
    Cc: Dave Hansen <dave@sr71.net>
    [ Prettified it a bit. ]
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
kernel.txt 23 KB