From: "Ahmed S. Darwish" <a.darwish@linutronix.de> To: Thomas Gleixner <tglx@linutronix.de>, Peter Zijlstra <peterz@infradead.org>, Leo Yan <leo.yan@linaro.org> Cc: Will Deacon <will@kernel.org>, John Ogness <jogness@linutronix.de>, "Sebastian A. Siewior" <bigeasy@linutronix.de>, LKML <linux-kernel@vger.kernel.org>, "Ahmed S. Darwish" <a.darwish@linutronix.de> Subject: [PATCH] time/sched_clock: Use raw_read_seqcount_latch() Date: Wed, 15 Jul 2020 13:59:01 +0200 Message-ID: <20200715115901.515956-1-a.darwish@linutronix.de> (raw) In-Reply-To: <20200715095220.GH10769@hirez.programming.kicks-ass.net> sched_clock uses seqcount_t latching to switch between two storage places protected by the sequence counter. This allows it to have interruptible, NMI-safe, seqcount_t write side critical sections. Since 7fc26327b756 ("seqlock: Introduce raw_read_seqcount_latch()"), raw_read_seqcount_latch() became the standardized way for seqcount_t latch read paths. Due to the dependent load, it also has one read memory barrier less than the currently used raw_read_seqcount() API. Use raw_read_seqcount_latch() for the seqcount_t latch read path. Link: https://lkml.kernel.org/r/20200625085745.GD117543@hirez.programming.kicks-ass.net Link: https://lkml.kernel.org/r/20200715092345.GA231464@debian-buster-darwi.lab.linutronix.de References: 1809bfa44e10 ("timers, sched/clock: Avoid deadlock during read from NMI") Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de> --- kernel/time/sched_clock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index fa3f800d7d76..ea007928d681 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -100,7 +100,7 @@ unsigned long long notrace sched_clock(void) struct clock_read_data *rd; do { - seq = raw_read_seqcount(&cd.seq); + seq = raw_read_seqcount_latch(&cd.seq); rd = cd.read_data + (seq & 1); cyc = (rd->read_sched_clock() - rd->epoch_cyc) & -- 2.20.1
next prev parent reply index Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-07-15 2:05 [PATCH v2 0/6] arm64: perf: Proper cap_user_time* support Leo Yan 2020-07-15 2:05 ` [PATCH v2 1/6] sched_clock: Expose struct clock_read_data Leo Yan 2020-07-15 5:56 ` Ahmed S. Darwish 2020-07-15 6:54 ` Leo Yan 2020-07-15 7:21 ` Ahmed S. Darwish 2020-07-15 8:12 ` Peter Zijlstra 2020-07-15 8:14 ` peterz 2020-07-15 9:23 ` Ahmed S. Darwish 2020-07-15 9:52 ` Peter Zijlstra 2020-07-15 11:59 ` Ahmed S. Darwish [this message] 2020-07-15 15:29 ` [PATCH] time/sched_clock: Use raw_read_seqcount_latch() Leo Yan 2020-07-15 15:58 ` Peter Zijlstra 2020-07-16 5:22 ` Leo Yan 2020-09-10 15:08 ` [tip: locking/core] time/sched_clock: Use raw_read_seqcount_latch() during suspend tip-bot2 for Ahmed S. Darwish 2020-07-15 2:05 ` [PATCH v2 2/6] arm64: perf: Implement correct cap_user_time Leo Yan 2020-07-15 8:38 ` Peter Zijlstra 2020-07-15 15:39 ` Leo Yan 2020-07-15 2:05 ` [PATCH v2 3/6] arm64: perf: Only advertise cap_user_time for arch_timer Leo Yan 2020-07-15 2:05 ` [PATCH v2 4/6] perf: Add perf_event_mmap_page::cap_user_time_short ABI Leo Yan 2020-07-15 2:05 ` [PATCH v2 5/6] arm64: perf: Add cap_user_time_short Leo Yan 2020-07-15 2:05 ` [PATCH v2 6/6] tools headers UAPI: Update tools's copy of linux/perf_event.h Leo Yan 2020-07-15 5:17 ` [PATCH v2 0/6] arm64: perf: Proper cap_user_time* support Ahmed S. Darwish 2020-07-15 6:29 ` Leo Yan
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