From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
[ Upstream commit 89e97eb8cec0f1af5ebf2380308913256ca7915a ]
The time order is incorrect when the TSC in a PEBS record is used.
$perf record -e cycles:upp dd if=/dev/zero of=/dev/null
count=10000
$ perf script --show-task-events
perf-exec 0 0.000000: PERF_RECORD_COMM: perf-exec:915/915
dd 915 106.479872: PERF_RECORD_COMM exec: dd:915/915
dd 915 106.483270: PERF_RECORD_EXIT(915:915):(914:914)
dd 915 106.512429: 1 cycles:upp:
ffffffff96c011b7 [unknown] ([unknown])
... ...
The perf time is from sched_clock_cpu(). The current PEBS code
unconditionally convert the TSC to native_sched_clock(). There is a
shift between the two clocks. If the TSC is stable, the shift is
consistent, __sched_clock_offset. If the TSC is unstable, the shift has
to be calculated at runtime.
This patch doesn't support the conversion when the TSC is unstable. The
TSC unstable case is a corner case and very unlikely to happen. If it
happens, the TSC in a PEBS record will be dropped and fall back to
perf_event_clock().
Fixes: 47a3aeb39e8d ("perf/x86/intel/pebs: Fix PEBS timestamps overwritten")
Reported-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/CAM9d7cgWDVAq8-11RbJ2uGfwkKD6fA-OMwOKDrNUrU_=8MgEjg@xxxxxxxxxxxxxx/
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/x86/events/intel/ds.c | 35 ++++++++++++++++++++++++++---------
1 file changed, 26 insertions(+), 9 deletions(-)
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 446d2833efa76..3ff38e7409e3d 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -2,12 +2,14 @@
#include <linux/bitops.h>
#include <linux/types.h>
#include <linux/slab.h>
+#include <linux/sched/clock.h>
#include <asm/cpu_entry_area.h>
#include <asm/perf_event.h>
#include <asm/tlbflush.h>
#include <asm/insn.h>
#include <asm/io.h>
+#include <asm/timer.h>
#include "../perf_event.h"
@@ -1519,6 +1521,27 @@ static u64 get_data_src(struct perf_event *event, u64 aux)
return val;
}
+static void setup_pebs_time(struct perf_event *event,
+ struct perf_sample_data *data,
+ u64 tsc)
+{
+ /* Converting to a user-defined clock is not supported yet. */
+ if (event->attr.use_clockid != 0)
+ return;
+
+ /*
+ * Doesn't support the conversion when the TSC is unstable.
+ * The TSC unstable case is a corner case and very unlikely to
+ * happen. If it happens, the TSC in a PEBS record will be
+ * dropped and fall back to perf_event_clock().
+ */
+ if (!using_native_sched_clock() || !sched_clock_stable())
+ return;
+
+ data->time = native_sched_clock_from_tsc(tsc) + __sched_clock_offset;
+ data->sample_flags |= PERF_SAMPLE_TIME;
+}
+
#define PERF_SAMPLE_ADDR_TYPE (PERF_SAMPLE_ADDR | \
PERF_SAMPLE_PHYS_ADDR | \
PERF_SAMPLE_DATA_PAGE_SIZE)
@@ -1668,11 +1691,8 @@ static void setup_pebs_fixed_sample_data(struct perf_event *event,
*
* We can only do this for the default trace clock.
*/
- if (x86_pmu.intel_cap.pebs_format >= 3 &&
- event->attr.use_clockid == 0) {
- data->time = native_sched_clock_from_tsc(pebs->tsc);
- data->sample_flags |= PERF_SAMPLE_TIME;
- }
+ if (x86_pmu.intel_cap.pebs_format >= 3)
+ setup_pebs_time(event, data, pebs->tsc);
if (has_branch_stack(event)) {
data->br_stack = &cpuc->lbr_stack;
@@ -1735,10 +1755,7 @@ static void setup_pebs_adaptive_sample_data(struct perf_event *event,
perf_sample_data_init(data, 0, event->hw.last_period);
data->period = event->hw.last_period;
- if (event->attr.use_clockid == 0) {
- data->time = native_sched_clock_from_tsc(basic->tsc);
- data->sample_flags |= PERF_SAMPLE_TIME;
- }
+ setup_pebs_time(event, data, basic->tsc);
/*
* We must however always use iregs for the unwinder to stay sane; the
--
2.39.2
