Messages in this thread | | | Date | Tue, 12 Feb 2013 09:42:50 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 4/5] perf, x86: Support full width counting v2 |
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* Andi Kleen <andi@firstfloor.org> wrote:
> From: Andi Kleen <ak@linux.intel.com> > > Recent Intel CPUs like Haswell and IvyBridge have a new alternative MSR > range for perfctrs that allows writing the full counter width. Enable this > range if the hardware reports it using a new capability bit. > > This lowers the overhead of perf stat slightly because it has to do less > interrupts to accumulate the counter value. On Haswell it also avoids some > problems with TSX aborting when the end of the counter range is reached. > > v2: Print the feature at boot > Reviewed-by: Stephane Eranian <eranian@google.com> > Signed-off-by: Andi Kleen <ak@linux.intel.com> > --- > arch/x86/include/uapi/asm/msr-index.h | 3 +++ > arch/x86/kernel/cpu/perf_event.h | 1 + > arch/x86/kernel/cpu/perf_event_intel.c | 7 +++++++ > 3 files changed, 11 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/include/uapi/asm/msr-index.h b/arch/x86/include/uapi/asm/msr-index.h > index 433a59f..af41a77 100644 > --- a/arch/x86/include/uapi/asm/msr-index.h > +++ b/arch/x86/include/uapi/asm/msr-index.h > @@ -163,6 +163,9 @@ > #define MSR_KNC_EVNTSEL0 0x00000028 > #define MSR_KNC_EVNTSEL1 0x00000029 > > +/* Alternative perfctr range with full access. */ > +#define MSR_IA32_PMC0 0x000004c1 > + > /* AMD64 MSRs. Not complete. See the architecture manual for a more > complete list. */ > > diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h > index ded4667..adaa0b0 100644 > --- a/arch/x86/kernel/cpu/perf_event.h > +++ b/arch/x86/kernel/cpu/perf_event.h > @@ -278,6 +278,7 @@ union perf_capabilities { > u64 pebs_arch_reg:1; > u64 pebs_format:4; > u64 smm_freeze:1; > + u64 fw_write:1;
No brownies for obfuscation: that should be named full_width_write, not a meaningless abbreviation that anyone crossing the code could mistake as 'firewall write' or 'forward write' or anything.
Also a comment line at the field should explain its meaning.
Thanks,
Ingo
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