Commit-ID: c48b60538c3ba05a7a2713c4791b25405525431b
Gitweb: http://git.kernel.org/tip/c48b60538c3ba05a7a2713c4791b25405525431b
Author: Vince Weaver <vweaver1@xxxxxxxxxxxx>
AuthorDate: Thu, 1 Mar 2012 17:28:14 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 6 Jun 2012 17:23:35 +0200
perf/x86: Use rdpmc() rather than rdmsr() when possible in the kernel
The rdpmc instruction is faster than the equivelant rdmsr call,
so use it when possible in the kernel.
The perfctr kernel patches did this, after extensive testing showed
rdpmc to always be faster (One can look in etc/costs in the perfctr-2.6
package to see a historical list of the overhead).
I have done some tests on a 3.2 kernel, the kernel module I used
was included in the first posting of this patch:
rdmsr rdpmc
Core2 T9900: 203.9 cycles 30.9 cycles
AMD fam0fh: 56.2 cycles 9.8 cycles
Atom 6/28/2: 129.7 cycles 50.6 cycles
The speedup of using rdpmc is large.
[ It's probably possible (and desirable) to do this without
requiring a new field in the hw_perf_event structure, but
the fixed events make this tricky. ]
Signed-off-by: Vince Weaver <vweaver1@xxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1203011724030.26934@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/cpu/perf_event.c | 4 +++-
include/linux/perf_event.h | 1 +
2 files changed, 4 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 43c2017..000a474 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -75,7 +75,7 @@ u64 x86_perf_event_update(struct perf_event *event)
*/
again:
prev_raw_count = local64_read(&hwc->prev_count);
- rdmsrl(hwc->event_base, new_raw_count);
+ rdpmcl(hwc->event_base_rdpmc, new_raw_count);
if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
new_raw_count) != prev_raw_count)
@@ -819,9 +819,11 @@ static inline void x86_assign_hw_event(struct perf_event *event,
} else if (hwc->idx >= X86_PMC_IDX_FIXED) {
hwc->config_base = MSR_ARCH_PERFMON_FIXED_CTR_CTRL;
hwc->event_base = MSR_ARCH_PERFMON_FIXED_CTR0 + (hwc->idx - X86_PMC_IDX_FIXED);
+ hwc->event_base_rdpmc = (hwc->idx - X86_PMC_IDX_FIXED) | 1<<30;
} else {
hwc->config_base = x86_pmu_config_addr(hwc->idx);
hwc->event_base = x86_pmu_event_addr(hwc->idx);
+ hwc->event_base_rdpmc = x86_pmu_addr_offset(hwc->idx);
}
}
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 45db49f..1ce887a 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -677,6 +677,7 @@ struct hw_perf_event {
u64 last_tag;
unsigned long config_base;
unsigned long event_base;
+ int event_base_rdpmc;
int idx;
int last_cpu;
--
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