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.
In V2, we improve reability of the comments.
Signed-off-by: Stephane Eranian <[email protected]>
---
arch/x86/events/intel/ds.c | 34 ++++++++++++++++++++++++----------
1 file changed, 24 insertions(+), 10 deletions(-)
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index da6780122786..e4e97fc8eec3 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 x86 EFLAGS 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;
@@ -1234,20 +1235,33 @@ 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 processors have eventing IP
+ * which avoids the off-by-1 skid. Use it when
+ * precise_ip >= 2
+ */
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: */
+ /*
+ * With precise_ip >= 2, try to fix up the off-by-1 IP
+ * using the LBR. If successful, the fixup function
+ * corrects regs->ip and calls set_linear_ip() on regs.
+ */
if (intel_pmu_pebs_fixup_ip(regs))
regs->flags |= PERF_EFLAGS_EXACT;
}
- } else
+ } else {
+ /*
+ * when precise_ip == 1, return the PEBS off-by-1 IP,
+ * no fixup attempted
+ */
set_linear_ip(regs, pebs->ip);
+ }
if ((sample_type & (PERF_SAMPLE_ADDR | PERF_SAMPLE_PHYS_ADDR)) &&
--
2.7.4
Commit-ID: d1e7e602cd64cf61f87dbf30df07c24df9eb1d99
Gitweb: https://git.kernel.org/tip/d1e7e602cd64cf61f87dbf30df07c24df9eb1d99
Author: Stephane Eranian <[email protected]>
AuthorDate: Wed, 4 Apr 2018 23:29:51 -0700
Committer: Ingo Molnar <[email protected]>
CommitDate: Thu, 5 Apr 2018 09:28:40 +0200
perf/x86/intel: Move regs->flags EXACT bit init
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.
Signed-off-by: Stephane Eranian <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
[ Improve capitalization, punctuation and clarity of comments. ]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/events/intel/ds.c | 34 ++++++++++++++++++++++++----------
1 file changed, 24 insertions(+), 10 deletions(-)
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index da6780122786..8a10a045b57b 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 x86 EFLAGS 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;
@@ -1234,20 +1235,33 @@ 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 processors have an 'eventing IP'
+ * (real IP) which fixes the off-by-1 skid in hardware.
+ * Use it when precise_ip >= 2 :
+ */
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: */
+ /*
+ * With precise_ip >= 2, try to fix up the off-by-1 IP
+ * using the LBR. If successful, the fixup function
+ * corrects regs->ip and calls set_linear_ip() on regs:
+ */
if (intel_pmu_pebs_fixup_ip(regs))
regs->flags |= PERF_EFLAGS_EXACT;
}
- } else
+ } else {
+ /*
+ * When precise_ip == 1, return the PEBS off-by-1 IP,
+ * no fixup attempted:
+ */
set_linear_ip(regs, pebs->ip);
+ }
if ((sample_type & (PERF_SAMPLE_ADDR | PERF_SAMPLE_PHYS_ADDR)) &&