linux-kernel - [PATCH v3 3/6] perf tsc: Calculate timestamp with cap_user_time

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Date:   Wed,  2 Sep 2020 14:21:28 +0100
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Wei Li <liwei391@...wei.com>,
        Al Grant <al.grant@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kemeng Shi <shikemeng@...wei.com>,
        Ian Rogers <irogers@...gle.com>,
        John Garry <john.garry@...wei.com>,
        Stephane Eranian <eranian@...gle.com>,
        Nick Gasson <nick.gasson@....com>,
        Andi Kleen <ak@...ux.intel.com>,
        Steve MacLean <Steve.MacLean@...rosoft.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Will Deacon <will@...nel.org>,
        James Clark <james.clark@....com>, linux-kernel@...r.kernel.org
Cc:     Leo Yan <leo.yan@...aro.org>
Subject: [PATCH v3 3/6] perf tsc: Calculate timestamp with cap_user_time_short

The perf mmap'ed buffer contains the flag 'cap_user_time_short' and two
extra fields 'time_cycles' and 'time_mask', perf tool needs to know
them for handling the counter wrapping case.

This patch is to reads out the relevant parameters from the head of the
first mmap'ed page and stores into the structure 'perf_tsc_conversion',
if the flag 'cap_user_time_short' has been set, it will firstly
calibrate cycle value for timestamp calculation.

Signed-off-by: Leo Yan <leo.yan@...aro.org>
---
 tools/perf/util/tsc.c | 12 +++++++++---
 tools/perf/util/tsc.h |  5 +++++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/tsc.c b/tools/perf/util/tsc.c
index 9e3f04ddddf8..c0ca40204649 100644
--- a/tools/perf/util/tsc.c
+++ b/tools/perf/util/tsc.c
@@ -28,6 +28,10 @@ u64 tsc_to_perf_time(u64 cyc, struct perf_tsc_conversion *tc)
 {
 	u64 quot, rem;
 
+	if (tc->cap_user_time_short)
+		cyc = tc->time_cycles +
+			((cyc - tc->time_cycles) & tc->time_mask);
+
 	quot = cyc >> tc->time_shift;
 	rem  = cyc & (((u64)1 << tc->time_shift) - 1);
 	return tc->time_zero + quot * tc->time_mult +
@@ -37,7 +41,6 @@ u64 tsc_to_perf_time(u64 cyc, struct perf_tsc_conversion *tc)
 int perf_read_tsc_conversion(const struct perf_event_mmap_page *pc,
 			     struct perf_tsc_conversion *tc)
 {
-	bool cap_user_time_zero;
 	u32 seq;
 	int i = 0;
 
@@ -47,7 +50,10 @@ int perf_read_tsc_conversion(const struct perf_event_mmap_page *pc,
 		tc->time_mult = pc->time_mult;
 		tc->time_shift = pc->time_shift;
 		tc->time_zero = pc->time_zero;
-		cap_user_time_zero = pc->cap_user_time_zero;
+		tc->time_cycles = pc->time_cycles;
+		tc->time_mask = pc->time_mask;
+		tc->cap_user_time_zero = pc->cap_user_time_zero;
+		tc->cap_user_time_short	= pc->cap_user_time_short;
 		rmb();
 		if (pc->lock == seq && !(seq & 1))
 			break;
@@ -57,7 +63,7 @@ int perf_read_tsc_conversion(const struct perf_event_mmap_page *pc,
 		}
 	}
 
-	if (!cap_user_time_zero)
+	if (!tc->cap_user_time_zero)
 		return -EOPNOTSUPP;
 
 	return 0;
diff --git a/tools/perf/util/tsc.h b/tools/perf/util/tsc.h
index 3c5a632ee57c..72a15419f3b3 100644
--- a/tools/perf/util/tsc.h
+++ b/tools/perf/util/tsc.h
@@ -8,6 +8,11 @@ struct perf_tsc_conversion {
 	u16 time_shift;
 	u32 time_mult;
 	u64 time_zero;
+	u64 time_cycles;
+	u64 time_mask;
+
+	bool cap_user_time_zero;
+	bool cap_user_time_short;
 };
 
 struct perf_event_mmap_page;
-- 
2.17.1