Messages in this thread Patch in this message | | | Date | Fri, 15 May 2009 08:42:30 GMT | From | tip-bot for Peter Zijlstra <> | Subject | [tip:perfcounters/core] perf_counter: x86: More accurate counter update |
| |
Commit-ID: ec3232bdf8518bea8410f0027f870b24d3aa8753 Gitweb: http://git.kernel.org/tip/ec3232bdf8518bea8410f0027f870b24d3aa8753 Author: Peter Zijlstra <a.p.zijlstra@chello.nl> AuthorDate: Wed, 13 May 2009 09:45:19 +0200 Committer: Ingo Molnar <mingo@elte.hu> CommitDate: Fri, 15 May 2009 09:46:54 +0200
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>
--- 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 f7772ff..3a92a2b 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);
| |