From: Leo Yan <leo.yan@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Ahmed S. Darwish" <a.darwish@linutronix.de>,
"Ben Dooks (Codethink)" <ben.dooks@codethink.co.uk>,
Paul Cercueil <paul@crapouillou.net>,
Adrian Hunter <adrian.hunter@intel.com>,
Kan Liang <kan.liang@linux.intel.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Cc: Leo Yan <leo.yan@linaro.org>
Subject: [PATCH v3 5/7] perf: Add perf_event_mmap_page::cap_user_time_short ABI
Date: Thu, 16 Jul 2020 13:11:28 +0800 [thread overview]
Message-ID: <20200716051130.4359-6-leo.yan@linaro.org> (raw)
In-Reply-To: <20200716051130.4359-1-leo.yan@linaro.org>
From: Peter Zijlstra <peterz@infradead.org>
In order to support short clock counters, provide an ABI extension.
As a whole:
u64 time, delta, cyc = read_cycle_counter();
+ if (cap_user_time_short)
+ cyc = time_cycle + ((cyc - time_cycle) & time_mask);
delta = mul_u64_u32_shr(cyc, time_mult, time_shift);
if (cap_user_time_zero)
time = time_zero + delta;
delta += time_offset;
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
include/uapi/linux/perf_event.h | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 7b2d6fc9e6ed..21a1edd08cbe 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -532,9 +532,10 @@ struct perf_event_mmap_page {
cap_bit0_is_deprecated : 1, /* Always 1, signals that bit 0 is zero */
cap_user_rdpmc : 1, /* The RDPMC instruction can be used to read counts */
- cap_user_time : 1, /* The time_* fields are used */
+ cap_user_time : 1, /* The time_{shift,mult,offset} fields are used */
cap_user_time_zero : 1, /* The time_zero field is used */
- cap_____res : 59;
+ cap_user_time_short : 1, /* the time_{cycle,mask} fields are used */
+ cap_____res : 58;
};
};
@@ -593,13 +594,29 @@ struct perf_event_mmap_page {
* ((rem * time_mult) >> time_shift);
*/
__u64 time_zero;
+
__u32 size; /* Header size up to __reserved[] fields. */
+ __u32 __reserved_1;
+
+ /*
+ * If cap_usr_time_short, the hardware clock is less than 64bit wide
+ * and we must compute the 'cyc' value, as used by cap_usr_time, as:
+ *
+ * cyc = time_cycles + ((cyc - time_cycles) & time_mask)
+ *
+ * NOTE: this form is explicitly chosen such that cap_usr_time_short
+ * is a correction on top of cap_usr_time, and code that doesn't
+ * know about cap_usr_time_short still works under the assumption
+ * the counter doesn't wrap.
+ */
+ __u64 time_cycles;
+ __u64 time_mask;
/*
* Hole for extension of the self monitor capabilities
*/
- __u8 __reserved[118*8+4]; /* align to 1k. */
+ __u8 __reserved[116*8]; /* align to 1k. */
/*
* Control data for the mmap() data buffer.
--
2.17.1
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next prev parent reply other threads:[~2020-07-16 5:13 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 5:11 [PATCH v3 0/7] arm64: perf: Proper cap_user_time* support Leo Yan
2020-07-16 5:11 ` [PATCH v3 1/7] sched_clock: Expose struct clock_read_data Leo Yan
2020-07-16 5:11 ` [PATCH v3 2/7] time/sched_clock: Use raw_read_seqcount_latch() Leo Yan
2020-07-16 5:11 ` [PATCH v3 3/7] arm64: perf: Implement correct cap_user_time Leo Yan
2020-07-16 5:11 ` [PATCH v3 4/7] arm64: perf: Only advertise cap_user_time for arch_timer Leo Yan
2020-07-16 5:11 ` Leo Yan [this message]
2020-07-16 5:11 ` [PATCH v3 6/7] arm64: perf: Add cap_user_time_short Leo Yan
2020-07-16 5:11 ` [PATCH v3 7/7] tools headers UAPI: Update tools's copy of linux/perf_event.h Leo Yan
2020-07-20 11:56 ` [PATCH v3 0/7] arm64: perf: Proper cap_user_time* support Will Deacon
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