[PATCH V4] POWER: perf_event: Skip updating kernel counters if register value shrinks

David Laight David.Laight at ACULAB.COM
Wed Apr 27 23:13:25 EST 2011

> prev and val are both 64 bit variables holding 32 bit numbers, we do
> accumulate in either, they are both replaced by values directly from
> registers.
> So prev > val will not always be true.

The code seems to be:
    prev = local64_read(&event->hw.prev_count);
    val = read_pmc(event->hw.idx);
    delta = check_and_compute_delta(prev, val);
    local64_add(delta, &event->count);
Which looks very much like 'prev' being a 64bit counter generated
from the 32bit pmc register.


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