Commit ec3232bd authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar

perf_counter: x86: More accurate counter update

Take the counter width into account instead of assuming 32 bits.

In particular Nehalem has 44 bit wide counters, and all
arithmetics should happen on a 44-bit signed integer basis.

[ Impact: fix rare event imprecision, warning message on Nehalem ]
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 1a853e36
...@@ -138,7 +138,9 @@ static u64 ...@@ -138,7 +138,9 @@ static u64
x86_perf_counter_update(struct perf_counter *counter, x86_perf_counter_update(struct perf_counter *counter,
struct hw_perf_counter *hwc, int idx) struct hw_perf_counter *hwc, int idx)
{ {
u64 prev_raw_count, new_raw_count, delta; int shift = 64 - x86_pmu.counter_bits;
u64 prev_raw_count, new_raw_count;
s64 delta;
/* /*
* Careful: an NMI might modify the previous counter value. * Careful: an NMI might modify the previous counter value.
...@@ -161,9 +163,10 @@ x86_perf_counter_update(struct perf_counter *counter, ...@@ -161,9 +163,10 @@ x86_perf_counter_update(struct perf_counter *counter,
* (counter-)time and add that to the generic counter. * (counter-)time and add that to the generic counter.
* *
* Careful, not all hw sign-extends above the physical width * Careful, not all hw sign-extends above the physical width
* of the count, so we do that by clipping the delta to 32 bits: * of the count.
*/ */
delta = (u64)(u32)((s32)new_raw_count - (s32)prev_raw_count); delta = (new_raw_count << shift) - (prev_raw_count << shift);
delta >>= shift;
atomic64_add(delta, &counter->count); atomic64_add(delta, &counter->count);
atomic64_sub(delta, &hwc->period_left); atomic64_sub(delta, &hwc->period_left);
......
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