redonkable
/
alistair23-linux
1
0
Fork 0
Code Releases Activity

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 294fe0f52a ("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: 294fe0f52a ("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>
hifive-unleashed-5.1
Kan Liang 2018-03-01 12:54:54 -05:00 committed by Ingo Molnar
parent 3f986eefc8
commit f605cfca8c
2 changed files with 2 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/events/intel/core.c
View File

@ -3188,7 +3188,7 @@ glp_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
* Therefore the effective (average) period matches the requested period,
* despite coarser hardware granularity.
*/
static unsigned bdw_limit_period(struct perf_event *event, unsigned left)
static u64 bdw_limit_period(struct perf_event *event, u64 left)
{
if ((event->hw.config & INTEL_ARCH_EVENT_MASK) ==
X86_CONFIG(.event=0xc0, .umask=0x01)) {

2
arch/x86/events/perf_event.h
View File

@ -557,7 +557,7 @@ struct x86_pmu {
struct x86_pmu_quirk *quirks;
int perfctr_second_write;
bool late_ack;
unsigned (*limit_period)(struct perf_event *event, unsigned l);
u64 (*limit_period)(struct perf_event *event, u64 l);
/*
* sysfs attrs