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perf/x86: Add ability to calculate TSC from perf sample timestamps

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For modern CPUs, perf clock is directly related to TSC.  TSC
can be calculated from perf clock and vice versa using a simple
calculation.  Two of the three componenets of that calculation
are already exported in struct perf_event_mmap_page.  This patch
exports the third.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: http://lkml.kernel.org/r/1372425741-1676-3-git-send-email-adrian.hunter@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Adrian Hunter 2013-06-28 16:22:18 +03:00 • committed by Ingo Molnar
parent 860f085b74
commit c73deb6aec
4 changed files with 33 additions and 2 deletions
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22
include/uapi/linux/perf_event.h
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@ -378,7 +378,8 @@ struct perf_event_mmap_page {
struct {
__u64 cap_usr_time : 1,
cap_usr_rdpmc : 1,
cap_____res : 62;
cap_usr_time_zero : 1,
cap_____res : 61;
};
};
@ -420,12 +421,29 @@ struct perf_event_mmap_page {
__u16 time_shift;
__u32 time_mult;
__u64 time_offset;
/*
* If cap_usr_time_zero, the hardware clock (e.g. TSC) can be calculated
* from sample timestamps.
*
* time = timestamp - time_zero;
* quot = time / time_mult;
* rem = time % time_mult;
* cyc = (quot << time_shift) + (rem << time_shift) / time_mult;
*
* And vice versa:
*
* quot = cyc >> time_shift;
* rem = cyc & ((1 << time_shift) - 1);
* timestamp = time_zero + quot * time_mult +
* ((rem * time_mult) >> time_shift);
*/
__u64 time_zero;
/*
* Hole for extension of the self monitor capabilities
*/
__u64 __reserved[120]; /* align to 1k */
__u64 __reserved[119]; /* align to 1k */
/*
* Control data for the mmap() data buffer.