powerpc/perf: Never program book3s PMCs with values >= 0x80000000
commit f56029410a
upstream.
We are seeing a lot of PMU warnings on POWER8:
Can't find PMC that caused IRQ
Looking closer, the active PMC is 0 at this point and we took a PMU
exception on the transition from negative to 0. Some versions of POWER8
have an issue where they edge detect and not level detect PMC overflows.
A number of places program the PMC with (0x80000000 - period_left),
where period_left can be negative. We can either fix all of these or
just ensure that period_left is always >= 1.
This patch takes the second option.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
8d706077c2
commit
3848c22cf6
|
@ -851,7 +851,22 @@ static void power_pmu_read(struct perf_event *event)
|
|||
} while (local64_cmpxchg(&event->hw.prev_count, prev, val) != prev);
|
||||
|
||||
local64_add(delta, &event->count);
|
||||
local64_sub(delta, &event->hw.period_left);
|
||||
|
||||
/*
|
||||
* A number of places program the PMC with (0x80000000 - period_left).
|
||||
* We never want period_left to be less than 1 because we will program
|
||||
* the PMC with a value >= 0x800000000 and an edge detected PMC will
|
||||
* roll around to 0 before taking an exception. We have seen this
|
||||
* on POWER8.
|
||||
*
|
||||
* To fix this, clamp the minimum value of period_left to 1.
|
||||
*/
|
||||
do {
|
||||
prev = local64_read(&event->hw.period_left);
|
||||
val = prev - delta;
|
||||
if (val < 1)
|
||||
val = 1;
|
||||
} while (local64_cmpxchg(&event->hw.period_left, prev, val) != prev);
|
||||
}
|
||||
|
||||
/*
|
||||
|
|
Loading…
Reference in New Issue