Re: [PATCH v3 1/3] perf: Use monotonic clock as a source for timestamps
On Tue, Nov 04, 2014 at 03:25:27PM +, Pawel Moll wrote:
> Very good idea, should have came up with it myself :-)
>
> Does __setup("perf_use_local_clock") sound reasonable?
Would not the 'module' already prefix a perf.? I never quite know how
all that works out. But sure, that works.
> Then we have to
> decide whether to hide the sysctl "perf_sample_time_clk_id" (my
> preferred option, will see how difficult it is) or just provide an
> invalid clock_id (eg. -1) in it.
invalid clock id is fine with me, although I suppose the clock people
might have an oh-pinion ;-)
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Re: [PATCH v3 1/3] perf: Use monotonic clock as a source for timestamps
On Tue, 2014-11-04 at 07:23 +, Peter Zijlstra wrote:
> On Tue, Nov 04, 2014 at 12:28:36AM +, Pawel Moll wrote:
>
> > +int sysctl_perf_sample_time_clk_id = CLOCK_MONOTONIC;
>
> const ?
Sure (unless we have to change it as mentioned below)
> > /*
> > * perf samples are done in some very critical code paths (NMIs).
> > * If they take too much CPU time, the system can lock up and not
> > @@ -324,7 +326,7 @@ extern __weak const char *perf_pmu_name(void)
> >
> > static inline u64 perf_clock(void)
> > {
> > - return local_clock();
> > + return ktime_get_mono_fast_ns();
> > }
>
> Do we maybe want to make it boot-time switchable back to local_clock for
> people with bad systems and or backwards compat issues?
Very good idea, should have came up with it myself :-)
Does __setup("perf_use_local_clock") sound reasonable? Then we have to
decide whether to hide the sysctl "perf_sample_time_clk_id" (my
preferred option, will see how difficult it is) or just provide an
invalid clock_id (eg. -1) in it.
Cheers!
Pawel
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Re: [PATCH v3 1/3] perf: Use monotonic clock as a source for timestamps
On Tue, 2014-11-04 at 07:23 +, Peter Zijlstra wrote:
On Tue, Nov 04, 2014 at 12:28:36AM +, Pawel Moll wrote:
+int sysctl_perf_sample_time_clk_id = CLOCK_MONOTONIC;
const ?
Sure (unless we have to change it as mentioned below)
/*
* perf samples are done in some very critical code paths (NMIs).
* If they take too much CPU time, the system can lock up and not
@@ -324,7 +326,7 @@ extern __weak const char *perf_pmu_name(void)
static inline u64 perf_clock(void)
{
- return local_clock();
+ return ktime_get_mono_fast_ns();
}
Do we maybe want to make it boot-time switchable back to local_clock for
people with bad systems and or backwards compat issues?
Very good idea, should have came up with it myself :-)
Does __setup(perf_use_local_clock) sound reasonable? Then we have to
decide whether to hide the sysctl perf_sample_time_clk_id (my
preferred option, will see how difficult it is) or just provide an
invalid clock_id (eg. -1) in it.
Cheers!
Pawel
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the body of a message to majord...@vger.kernel.org
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Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH v3 1/3] perf: Use monotonic clock as a source for timestamps
On Tue, Nov 04, 2014 at 03:25:27PM +, Pawel Moll wrote: Very good idea, should have came up with it myself :-) Does __setup(perf_use_local_clock) sound reasonable? Would not the 'module' already prefix a perf.? I never quite know how all that works out. But sure, that works. Then we have to decide whether to hide the sysctl perf_sample_time_clk_id (my preferred option, will see how difficult it is) or just provide an invalid clock_id (eg. -1) in it. invalid clock id is fine with me, although I suppose the clock people might have an oh-pinion ;-) -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH v3 1/3] perf: Use monotonic clock as a source for timestamps
On Tue, Nov 04, 2014 at 12:28:36AM +, Pawel Moll wrote:
> +int sysctl_perf_sample_time_clk_id = CLOCK_MONOTONIC;
const ?
> /*
> * perf samples are done in some very critical code paths (NMIs).
> * If they take too much CPU time, the system can lock up and not
> @@ -324,7 +326,7 @@ extern __weak const char *perf_pmu_name(void)
>
> static inline u64 perf_clock(void)
> {
> - return local_clock();
> + return ktime_get_mono_fast_ns();
> }
Do we maybe want to make it boot-time switchable back to local_clock for
people with bad systems and or backwards compat issues?
Everybody using Core2 and older will very much not want to have this
unless they've got a very good reason for wanting it.
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Re: [PATCH v3 1/3] perf: Use monotonic clock as a source for timestamps
On Tue, Nov 04, 2014 at 12:28:36AM +, Pawel Moll wrote:
+int sysctl_perf_sample_time_clk_id = CLOCK_MONOTONIC;
const ?
/*
* perf samples are done in some very critical code paths (NMIs).
* If they take too much CPU time, the system can lock up and not
@@ -324,7 +326,7 @@ extern __weak const char *perf_pmu_name(void)
static inline u64 perf_clock(void)
{
- return local_clock();
+ return ktime_get_mono_fast_ns();
}
Do we maybe want to make it boot-time switchable back to local_clock for
people with bad systems and or backwards compat issues?
Everybody using Core2 and older will very much not want to have this
unless they've got a very good reason for wanting it.
--
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the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
