diff options
| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2009-05-13 09:45:19 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-05-15 09:46:54 +0200 |
| commit | ec3232bdf8518bea8410f0027f870b24d3aa8753 (patch) | |
| tree | 5aa20585dfec4053f92f5da5ae7488b13a8bebb4 /arch | |
| parent | 1a853e36871b533ccc3f3c5bdd5cd0d867043a00 (diff) | |
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: Peter 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: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/cpu/perf_counter.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c index f7772ff7936..3a92a2b2a80 100644 --- a/arch/x86/kernel/cpu/perf_counter.c +++ b/arch/x86/kernel/cpu/perf_counter.c @@ -138,7 +138,9 @@ static u64 x86_perf_counter_update(struct perf_counter *counter, 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. @@ -161,9 +163,10 @@ again: * (counter-)time and add that to the generic counter. * * 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_sub(delta, &hwc->period_left); |