• Arjan van de Ven's avatar
    x86, timers: Check for pending timers after (device) interrupts · 9bcbdd9c
    Arjan van de Ven authored
    Now that range timers and deferred timers are common, I found a
    problem with these using the "perf timechart" tool. Frans Pop also
    reported high scheduler latencies via LatencyTop, when using
    iwlagn.
    
    It turns out that on x86, these two 'opportunistic' timers only get
    checked when another "real" timer happens. These opportunistic
    timers have the objective to save power by hitchhiking on other
    wakeups, as to avoid CPU wakeups by themselves as much as possible.
    
    The change in this patch runs this check not only at timer
    interrupts, but at all (device) interrupts. The effect is that:
    
     1) the deferred timers/range timers get delayed less
    
     2) the range timers cause less wakeups by themselves because
        the percentage of hitchhiking on existing wakeup events goes up.
    
    I've verified the working of the patch using "perf timechart", the
    original exposed bug is gone with this patch. Frans also reported
    success - the latencies are now down in the expected ~10 msec
    range.
    Signed-off-by: default avatarArjan van de Ven <arjan@linux.intel.com>
    Tested-by: default avatarFrans Pop <elendil@planet.nl>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Mike Galbraith <efault@gmx.de>
    LKML-Reference: <20091008064041.67219b13@infradead.org>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    9bcbdd9c
smp.c 6.82 KB