linux-kernel - [PATCH V2] perf/x86/intel/ds: Fix the conversion from TSC to perf time

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Message-Id: <20230125204925.924442-1-kan.liang@linux.intel.com>
Date:   Wed, 25 Jan 2023 12:49:25 -0800
From:   kan.liang@...ux.intel.com
To:     peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     namhyung@...nel.org, eranian@...gle.com, ak@...ux.intel.com,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: [PATCH V2] perf/x86/intel/ds: Fix the conversion from TSC to perf time

From: Kan Liang <kan.liang@...ux.intel.com>

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@...nel.org>
Link: https://lore.kernel.org/all/CAM9d7cgWDVAq8-11RbJ2uGfwkKD6fA-OMwOKDrNUrU_=8MgEjg@mail.gmail.com/
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
---

Changes since V1:
- Update the comments and description to avoid the confusion.

 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 183efa914b99..b0354dc869d2 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"
 
@@ -1568,6 +1570,27 @@ 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)
@@ -1715,11 +1738,8 @@ 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))
 		perf_sample_save_brstack(data, event, &cpuc->lbr_stack);
@@ -1781,10 +1801,7 @@ 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
-- 
2.35.1