linux-kernel - [PATCH v4 2/6] perf tsc: Add rdtsc() for Arm64

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Date:   Mon, 14 Sep 2020 19:53:07 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kemeng Shi <shikemeng@...wei.com>,
        Ian Rogers <irogers@...gle.com>,
        Remi Bernon <rbernon@...eweavers.com>,
        Nick Gasson <nick.gasson@....com>,
        Stephane Eranian <eranian@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Steve MacLean <Steve.MacLean@...rosoft.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Zou Wei <zou_wei@...wei.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Cc:     Leo Yan <leo.yan@...aro.org>
Subject: [PATCH v4 2/6] perf tsc: Add rdtsc() for Arm64

The system register CNTVCT_EL0 can be used to retrieve the counter from
user space.  Add rdtsc() for Arm64.

Signed-off-by: Leo Yan <leo.yan@...aro.org>
---
 tools/perf/arch/arm64/util/Build |  1 +
 tools/perf/arch/arm64/util/tsc.c | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 tools/perf/arch/arm64/util/tsc.c

diff --git a/tools/perf/arch/arm64/util/Build b/tools/perf/arch/arm64/util/Build
index 5c13438c7bd4..b53294d74b01 100644
--- a/tools/perf/arch/arm64/util/Build
+++ b/tools/perf/arch/arm64/util/Build
@@ -1,6 +1,7 @@
 perf-y += header.o
 perf-y += machine.o
 perf-y += perf_regs.o
+perf-y += tsc.o
 perf-$(CONFIG_DWARF)     += dwarf-regs.o
 perf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
 perf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
diff --git a/tools/perf/arch/arm64/util/tsc.c b/tools/perf/arch/arm64/util/tsc.c
new file mode 100644
index 000000000000..cc85bd9e73f1
--- /dev/null
+++ b/tools/perf/arch/arm64/util/tsc.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/types.h>
+
+#include "../../../util/tsc.h"
+
+u64 rdtsc(void)
+{
+	u64 val;
+
+	/*
+	 * According to ARM DDI 0487F.c, from Armv8.0 to Armv8.5 inclusive, the
+	 * system counter is at least 56 bits wide; from Armv8.6, the counter
+	 * must be 64 bits wide.  So the system counter could be less than 64
+	 * bits wide and it is attributed with the flag 'cap_user_time_short'
+	 * is true.
+	 */
+	asm volatile("mrs %0, cntvct_el0" : "=r" (val));
+
+	return val;
+}
-- 
2.17.1