diff options
| author | Paul Mackerras <paulus@samba.org> | 2009-03-23 18:22:08 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-04-06 09:30:26 +0200 |
| commit | 37d81828385f8ff823caaaf1a83e72d065b6cfa1 (patch) | |
| tree | 972900a193a6a5ab1bdc14adcd7ab72bf0a51c13 /arch | |
| parent | 96f6d4444302bb2ea2cf409529eef816462f6ce0 (diff) | |
perf_counter: add an mmap method to allow userspace to read hardware counters
Impact: new feature giving performance improvement
This adds the ability for userspace to do an mmap on a hardware counter
fd and get access to a read-only page that contains the information
needed to translate a hardware counter value to the full 64-bit
counter value that would be returned by a read on the fd. This is
useful on architectures that allow user programs to read the hardware
counters, such as PowerPC.
The mmap will only succeed if the counter is a hardware counter
monitoring the current process.
On my quad 2.5GHz PowerPC 970MP machine, userspace can read a counter
and translate it to the full 64-bit value in about 30ns using the
mmapped page, compared to about 830ns for the read syscall on the
counter, so this does give a significant performance improvement.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Orig-LKML-Reference: <20090323172417.297057964@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/powerpc/kernel/perf_counter.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c index d05651584d4..e4349281b07 100644 --- a/arch/powerpc/kernel/perf_counter.c +++ b/arch/powerpc/kernel/perf_counter.c @@ -417,6 +417,8 @@ void hw_perf_restore(u64 disable) atomic64_set(&counter->hw.prev_count, val); counter->hw.idx = hwc_index[i] + 1; write_pmc(counter->hw.idx, val); + if (counter->user_page) + perf_counter_update_userpage(counter); } mb(); cpuhw->mmcr[0] |= MMCR0_PMXE | MMCR0_FCECE; @@ -572,6 +574,8 @@ static void power_perf_disable(struct perf_counter *counter) ppmu->disable_pmc(counter->hw.idx - 1, cpuhw->mmcr); write_pmc(counter->hw.idx, 0); counter->hw.idx = 0; + if (counter->user_page) + perf_counter_update_userpage(counter); break; } } @@ -698,6 +702,8 @@ static void record_and_restart(struct perf_counter *counter, long val, write_pmc(counter->hw.idx, val); atomic64_set(&counter->hw.prev_count, val); atomic64_set(&counter->hw.period_left, left); + if (counter->user_page) + perf_counter_update_userpage(counter); /* * Finally record data if requested. |