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Subject[tip:perf/core] perf, x86: Make a second write to performance counter if needed
Commit-ID:  68aa00ac0a82e9a876c799bf6be7622b8f1c8517
Gitweb: http://git.kernel.org/tip/68aa00ac0a82e9a876c799bf6be7622b8f1c8517
Author: Cyrill Gorcunov <gorcunov@openvz.org>
AuthorDate: Thu, 3 Jun 2010 01:23:04 +0400
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 9 Jun 2010 11:12:35 +0200

perf, x86: Make a second write to performance counter if needed

On Netburst PMU we need a second write to a performance counter
due to cpu erratum.

A simple flag test instead of alternative instructions was choosen
because wrmsrl is already a macro and if virtualization is turned
on will need an additional wrapper call which is more expencise.

nb: we should propably switch to jump-labels as only this facility
reach the mainline.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Lin Ming <ming.m.lin@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20100602212304.GC5264@lenovo>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/cpu/perf_event.c | 12 +++++++++++-
arch/x86/kernel/cpu/perf_event_p4.c | 9 +++++++++
2 files changed, 20 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index af04c6f..79e1998 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -220,6 +220,7 @@ struct x86_pmu {
struct perf_event *event);
struct event_constraint *event_constraints;
void (*quirks)(void);
+ int perfctr_second_write;

int (*cpu_prepare)(int cpu);
void (*cpu_starting)(int cpu);
@@ -925,8 +926,17 @@ x86_perf_event_set_period(struct perf_event *event)
*/
atomic64_set(&hwc->prev_count, (u64)-left);

- wrmsrl(hwc->event_base + idx,
+ wrmsrl(hwc->event_base + idx, (u64)(-left) & x86_pmu.cntval_mask);
+
+ /*
+ * Due to erratum on certan cpu we need
+ * a second write to be sure the register
+ * is updated properly
+ */
+ if (x86_pmu.perfctr_second_write) {
+ wrmsrl(hwc->event_base + idx,
(u64)(-left) & x86_pmu.cntval_mask);
+ }

perf_event_update_userpage(event);

diff --git a/arch/x86/kernel/cpu/perf_event_p4.c b/arch/x86/kernel/cpu/perf_event_p4.c
index ae85d69..9286e73 100644
--- a/arch/x86/kernel/cpu/perf_event_p4.c
+++ b/arch/x86/kernel/cpu/perf_event_p4.c
@@ -829,6 +829,15 @@ static __initconst const struct x86_pmu p4_pmu = {
.max_period = (1ULL << 39) - 1,
.hw_config = p4_hw_config,
.schedule_events = p4_pmu_schedule_events,
+ /*
+ * This handles erratum N15 in intel doc 249199-029,
+ * the counter may not be updated correctly on write
+ * so we need a second write operation to do the trick
+ * (the official workaround didn't work)
+ *
+ * the former idea is taken from OProfile code
+ */
+ .perfctr_second_write = 1,
};

static __init int p4_pmu_init(void)

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