This patch removes a redundant store on regs->flags introduced
by commit:
71eb9ee9596d ("perf/x86/intel: Fix linear IP of PEBS real_ip on Haswell and
later CPUs")
We were clearing the PERF_EFLAGS_EXACT but it was overwritten by
regs->flags = pebs->flags later on.
The PERF_EFLAGS_EXACT is a software flag using bit 3 of regs->flags.
X86 marks this bit as Reserved. To make sure this bit is zero before
we do any IP processing, we clear it explicitly.
Patch also removes the following assignment:
regs->flags = pebs->flags | (regs->flags & PERF_EFLAGS_VM);
Because there is no regs->flags to preserve anymore because
set_linear_ip() is not called until later.
Patch also clarifies comment for intel_pmu_pebs_fixup_ip().
Signed-off-by: Stephane Eranian <eran...@google.com>
---
arch/x86/events/intel/ds.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index da6780122786..41b44a4fff51 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1153,7 +1153,6 @@ static void setup_pebs_sample_data(struct perf_event
*event,
if (pebs == NULL)
return;
- regs->flags &= ~PERF_EFLAGS_EXACT;
sample_type = event->attr.sample_type;
dsrc = sample_type & PERF_SAMPLE_DATA_SRC;
@@ -1197,7 +1196,13 @@ static void setup_pebs_sample_data(struct perf_event
*event,
* and PMI.
*/
*regs = *iregs;
- regs->flags = pebs->flags;
+
+ /*
+ * initialize regs_>flags from pebs
+ * clear exact bit (which uses Reserved bit 3),
+ * i.e, do not rely on it being zero.
+ */
+ regs->flags = pebs->flags & ~PERF_EFLAGS_EXACT;
if (sample_type & PERF_SAMPLE_REGS_INTR) {
regs->ax = pebs->ax;
@@ -1217,10 +1222,6 @@ static void setup_pebs_sample_data(struct perf_event
*event,
regs->sp = pebs->sp;
}
- /*
- * Preserve PERF_EFLAGS_VM from set_linear_ip().
- */
- regs->flags = pebs->flags | (regs->flags & PERF_EFLAGS_VM);
#ifndef CONFIG_X86_32
regs->r8 = pebs->r8;
regs->r9 = pebs->r9;
@@ -1234,15 +1235,19 @@ static void setup_pebs_sample_data(struct perf_event
*event,
}
if (event->attr.precise_ip > 1) {
- /* Haswell and later have the eventing IP, so use it: */
+ /* Haswell and later have the eventing IP, so use it */
if (x86_pmu.intel_cap.pebs_format >= 2) {
set_linear_ip(regs, pebs->real_ip);
regs->flags |= PERF_EFLAGS_EXACT;
} else {
- /* Otherwise use PEBS off-by-1 IP: */
+ /* Otherwise use PEBS off-by-1 IP */
set_linear_ip(regs, pebs->ip);
- /* ... and try to fix it up using the LBR entries: */
+ /*
+ * ... and try to fix it up using the LBR entries
+ * if successful, regs->ip modified and regs patch
+ * via set_linear_ip()
+ */
if (intel_pmu_pebs_fixup_ip(regs))
regs->flags |= PERF_EFLAGS_EXACT;
}
--
2.7.4
