perf/x86/intel: Fix large period handling on Broadwell CPUs
authorKan Liang <kan.liang@linux.intel.com>
Thu, 1 Mar 2018 17:54:54 +0000 (12:54 -0500)
committerIngo Molnar <mingo@kernel.org>
Fri, 9 Mar 2018 07:22:05 +0000 (08:22 +0100)
commitf605cfca8c39ffa2b98c06d2b9f30ba64f1e54e3
tree14fedd7100c8a1f4947beecbb6a05f92c804a6a2
parent3f986eefc89c528bf2d398a6dc3637b743a7139e
perf/x86/intel: Fix large period handling on Broadwell CPUs

Large fixed period values could be truncated on Broadwell, for example:

  perf record -e cycles -c 10000000000

Here the fixed period is 0x2540BE400, but the period which finally applied is
0x540BE400 - which is wrong.

The reason is that x86_pmu::limit_period() uses an u32 parameter, so the
high 32 bits of 'period' get truncated.

This bug was introduced in:

  commit 294fe0f52a44 ("perf/x86/intel: Add INST_RETIRED.ALL workarounds")

It's safe to use u64 instead of u32:

 - Although the 'left' is s64, the value of 'left' must be positive when
   calling limit_period().

 - bdw_limit_period() only modifies the lowest 6 bits, it doesn't touch
   the higher 32 bits.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.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: 294fe0f52a44 ("perf/x86/intel: Add INST_RETIRED.ALL workarounds")
Link: http://lkml.kernel.org/r/1519926894-3520-1-git-send-email-kan.liang@linux.intel.com
[ Rewrote unacceptably bad changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
arch/x86/events/intel/core.c
arch/x86/events/perf_event.h