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| author | Adrian Hunter | 2013-06-28 15:22:18 +0200 |
|---|---|---|
| committer | Ingo Molnar | 2013-07-23 12:17:45 +0200 |
| commit | c73deb6aecda2955716f31572516f09d930ef450 (patch) | |
| tree | 037f7945cb4289545d5ffbe9506e071a83d6c1a6 /include/uapi/linux/perf_event.h | |
| parent | perf: Fix broken union in 'struct perf_event_mmap_page' (diff) | |
| download | kernel-qcow2-linux-c73deb6aecda2955716f31572516f09d930ef450.tar.gz kernel-qcow2-linux-c73deb6aecda2955716f31572516f09d930ef450.tar.xz kernel-qcow2-linux-c73deb6aecda2955716f31572516f09d930ef450.zip | |
perf/x86: Add ability to calculate TSC from perf sample timestamps
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>
Diffstat (limited to 'include/uapi/linux/perf_event.h')
| -rw-r--r-- | include/uapi/linux/perf_event.h | 22 |
1 files changed, 20 insertions, 2 deletions
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h index 0041aedf2297..efef1d37a371 100644 --- a/include/uapi/linux/perf_event.h +++ b/include/uapi/linux/perf_event.h @@ -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. |