From: "Ahmed S. Darwish" <a.darwish@linutronix.de> To: Leo Yan <leo.yan@linaro.org>, Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Ingo Molnar <mingo@redhat.com>, Arnaldo Carvalho de Melo <acme@kernel.org>, 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>, Paul Cercueil <paul@crapouillou.net>, "Ben Dooks (Codethink)" <ben.dooks@codethink.co.uk>, Adrian Hunter <adrian.hunter@intel.com>, Kan Liang <kan.liang@linux.intel.com>, jogness@linutronix.de, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/6] sched_clock: Expose struct clock_read_data Date: Wed, 15 Jul 2020 07:56:50 +0200 [thread overview] Message-ID: <20200715055650.GB225020@debian-buster-darwi.lab.linutronix.de> (raw) In-Reply-To: <20200715020512.20991-2-leo.yan@linaro.org> On Wed, Jul 15, 2020 at 10:05:07AM +0800, Leo Yan wrote: > From: Peter Zijlstra <peterz@infradead.org> > ... > > Provide struct clock_read_data and two (seqcount) helpers so that > architectures (arm64 in specific) can expose the numbers to userspace. > ... > > +struct clock_read_data *sched_clock_read_begin(unsigned int *seq) > +{ > + *seq = raw_read_seqcount(&cd.seq); > + return cd.read_data + (*seq & 1); > +} > + ... Hmm, this seqcount_t is actually a latch seqcount. I know the original code also used raw_read_seqcount(), but while at it, let's use the proper read API for seqcount_t latchers: raw_read_seqcount_latch(). raw_read_seqcount_latch() has no read memory barrier though, and a suspicious claim that READ_ONCE() pairs with an smp_wmb() (??). But if its implementation is wrong, let's fix it there instead. Thanks, -- Ahmed S. Darwish Linutronix GmbH
WARNING: multiple messages have this Message-ID (diff)
From: "Ahmed S. Darwish" <a.darwish@linutronix.de> To: Leo Yan <leo.yan@linaro.org>, Peter Zijlstra <peterz@infradead.org> Cc: Mark Rutland <mark.rutland@arm.com>, Alexander Shishkin <alexander.shishkin@linux.intel.com>, Will Deacon <will@kernel.org>, Adrian Hunter <adrian.hunter@intel.com>, Arnaldo Carvalho de Melo <acme@kernel.org>, linux-kernel@vger.kernel.org, Paul Cercueil <paul@crapouillou.net>, Ingo Molnar <mingo@redhat.com>, Catalin Marinas <catalin.marinas@arm.com>, Namhyung Kim <namhyung@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, jogness@linutronix.de, Jiri Olsa <jolsa@redhat.com>, "Ben Dooks \(Codethink\)" <ben.dooks@codethink.co.uk>, linux-arm-kernel@lists.infradead.org, Kan Liang <kan.liang@linux.intel.com> Subject: Re: [PATCH v2 1/6] sched_clock: Expose struct clock_read_data Date: Wed, 15 Jul 2020 07:56:50 +0200 [thread overview] Message-ID: <20200715055650.GB225020@debian-buster-darwi.lab.linutronix.de> (raw) In-Reply-To: <20200715020512.20991-2-leo.yan@linaro.org> On Wed, Jul 15, 2020 at 10:05:07AM +0800, Leo Yan wrote: > From: Peter Zijlstra <peterz@infradead.org> > ... > > Provide struct clock_read_data and two (seqcount) helpers so that > architectures (arm64 in specific) can expose the numbers to userspace. > ... > > +struct clock_read_data *sched_clock_read_begin(unsigned int *seq) > +{ > + *seq = raw_read_seqcount(&cd.seq); > + return cd.read_data + (*seq & 1); > +} > + ... Hmm, this seqcount_t is actually a latch seqcount. I know the original code also used raw_read_seqcount(), but while at it, let's use the proper read API for seqcount_t latchers: raw_read_seqcount_latch(). raw_read_seqcount_latch() has no read memory barrier though, and a suspicious claim that READ_ONCE() pairs with an smp_wmb() (??). But if its implementation is wrong, let's fix it there instead. Thanks, -- Ahmed S. Darwish Linutronix GmbH _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-07-15 5:56 UTC|newest] Thread overview: 41+ 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 ` Leo Yan 2020-07-15 2:05 ` [PATCH v2 1/6] sched_clock: Expose struct clock_read_data Leo Yan 2020-07-15 2:05 ` Leo Yan 2020-07-15 5:56 ` Ahmed S. Darwish [this message] 2020-07-15 5:56 ` Ahmed S. Darwish 2020-07-15 6:54 ` Leo Yan 2020-07-15 6:54 ` Leo Yan 2020-07-15 7:21 ` Ahmed S. Darwish 2020-07-15 7:21 ` Ahmed S. Darwish 2020-07-15 8:12 ` Peter Zijlstra 2020-07-15 8:12 ` Peter Zijlstra 2020-07-15 8:14 ` peterz 2020-07-15 8:14 ` peterz 2020-07-15 9:23 ` Ahmed S. Darwish 2020-07-15 9:23 ` Ahmed S. Darwish 2020-07-15 9:52 ` Peter Zijlstra 2020-07-15 9:52 ` Peter Zijlstra 2020-07-15 11:59 ` [PATCH] time/sched_clock: Use raw_read_seqcount_latch() Ahmed S. Darwish 2020-07-15 15:29 ` 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 2:05 ` Leo Yan 2020-07-15 8:38 ` Peter Zijlstra 2020-07-15 8:38 ` Peter Zijlstra 2020-07-15 15:39 ` Leo Yan 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 ` 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 ` 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 ` 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 2:05 ` Leo Yan 2020-07-15 5:17 ` [PATCH v2 0/6] arm64: perf: Proper cap_user_time* support Ahmed S. Darwish 2020-07-15 5:17 ` Ahmed S. Darwish 2020-07-15 6:29 ` Leo Yan 2020-07-15 6:29 ` Leo Yan
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