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Adrian Hunter b9511cd761 perf/x86: Fix time_shift in perf_event_mmap_page 
Commit:

  b20112edea ("perf/x86: Improve accuracy of perf/sched clock")

allowed the time_shift value in perf_event_mmap_page to be as much
as 32.  Unfortunately the documented algorithms for using time_shift
have it shifting an integer, whereas to work correctly with the value
32, the type must be u64.

In the case of perf tools, Intel PT decodes correctly but the timestamps
that are output (for example by perf script) have lost 32-bits of
granularity so they look like they are not changing at all.

Fix by limiting the shift to 31 and adjusting the multiplier accordingly.

Also update the documentation of perf_event_mmap_page so that new code
based on it will be more future-proof.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: b20112edea ("perf/x86: Improve accuracy of perf/sched clock")
Link: http://lkml.kernel.org/r/1445001845-13688-2-git-send-email-adrian.hunter@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-10-20 10:30:52 +02:00
..
acpi ACPI: Eliminate CONFIG_.*{, _MODULE} #ifdef in favor of IS_ENABLED() 2015-09-15 03:05:45 +02:00
asm-generic Merge branch 'strscpy' of git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile 2015-10-04 16:31:13 +01:00
clocksource
crypto Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2015-09-08 12:41:25 -07:00
drm drm/dp/mst: add some defines for logical/physical ports 2015-10-02 15:34:42 +10:00
dt-bindings Merge branch 'drivers/reset' into next/late 2015-09-09 15:42:45 -07:00
keys
kvm arm/arm64: KVM: Remove 'config KVM_ARM_MAX_VCPUS' 2015-09-17 13:13:27 +01:00
linux Merge branch 'perf/urgent' into perf/core, before pulling new changes 2015-10-08 10:52:18 +02:00
math-emu
media media updates for v4.3-rc1 2015-09-11 16:42:39 -07:00
memory
misc cxl: Allow the kernel to trust that an image won't change on PERST. 2015-08-14 21:32:07 +10:00
net af_unix: Convert the unix_sk macro to an inline function for type safety 2015-09-29 13:47:07 -07:00
pcmcia
ras
rdma Changes for 4.3-rc1 2015-09-19 20:04:11 -07:00
rxrpc
scsi Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending 2015-09-11 19:00:42 -07:00
soc IOMMU Updates for Linux v4.3 2015-09-08 17:22:35 -07:00
sound ALSA: hda - Fix missing inline for dummy snd_hdac_set_codec_wakeup() 2015-09-02 12:24:55 +02:00
target target: Propigate backend read-only to core_tpg_add_lun 2015-09-24 23:17:21 -07:00
trace Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/rzhang/linux 2015-09-11 16:13:47 -07:00
uapi perf/x86: Fix time_shift in perf_event_mmap_page 2015-10-20 10:30:52 +02:00
video libnvdimm for 4.3: 2015-09-08 14:35:59 -07:00
xen x86/xen: Support kexec/kdump in HVM guests by doing a soft reset 2015-09-28 14:48:52 +01:00
Kbuild