From: "Ahmed S. Darwish" <a.darwish@linutronix.de> To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de>, "Sebastian A. Siewior" <bigeasy@linutronix.de>, "Paul E. McKenney" <paulmck@kernel.org>, Steven Rostedt <rostedt@goodmis.org>, LKML <linux-kernel@vger.kernel.org>, "Ahmed S. Darwish" <a.darwish@linutronix.de> Subject: [PATCH v2 0/5] seqlock: Introduce PREEMPT_RT support Date: Fri, 4 Sep 2020 17:32:26 +0200 Message-ID: <20200904153231.11994-1-a.darwish@linutronix.de> (raw) Hi, Changelog-v2 ============ - Standardize on seqcount_LOCKNAME_t as the canonical reference for sequence counters with associated locks, instead of v1 seqcount_LOCKTYPE_t. - Use unique prefix "seqprop_*" for all seqcount_t/seqcount_LOCKNAME_t property accessors. - Touch-up the lock-unlock rationale for more clarity. Enforce writer non-preemitiblity using "__seq_enforce_writer_non_preemptibility()". Cover letter (v1) ================= https://lkml.kernel.org/r/20200828010710.5407-1-a.darwish@linutronix.de Preemption must be disabled before entering a sequence counter write side critical section. Otherwise the read side section can preempt the write side section and spin for the entire scheduler tick. If that reader belongs to a real-time scheduling class, it can spin forever and the kernel will livelock. Disabling preemption cannot be done for PREEMPT_RT though: it can lead to higher latencies, and the write side sections will not be able to acquire locks which become sleeping locks (e.g. spinlock_t). To remain preemptible, while avoiding a possible livelock caused by the reader preempting the writer, use a different technique: let the reader detect if a seqcount_LOCKNAME_t writer is in progress. If that's the case, acquire then release the associated LOCKNAME writer serialization lock. This will allow any possibly-preempted writer to make progress until the end of its writer serialization lock critical section. Implement this lock-unlock technique for all seqcount_LOCKNAME_t with an associated (PREEMPT_RT) sleeping lock, and for seqlock_t. 8<-------------- Ahmed S. Darwish (5): seqlock: seqcount_LOCKNAME_t: Standardize naming convention seqlock: Use unique prefix for seqcount_t property accessors seqlock: seqcount_t: Implement all read APIs as statement expressions seqlock: seqcount_LOCKNAME_t: Introduce PREEMPT_RT support seqlock: PREEMPT_RT: Do not starve seqlock_t writers include/linux/seqlock.h | 281 ++++++++++++++++++++++++---------------- 1 file changed, 167 insertions(+), 114 deletions(-) base-commit: f75aef392f869018f78cfedf3c320a6b3fcfda6b -- 2.28.0
next reply index Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-09-04 15:32 Ahmed S. Darwish [this message] 2020-09-04 15:32 ` [PATCH v2 1/5] seqlock: seqcount_LOCKNAME_t: Standardize naming convention Ahmed S. Darwish 2020-09-10 15:08 ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish 2020-09-04 15:32 ` [PATCH v2 2/5] seqlock: Use unique prefix for seqcount_t property accessors Ahmed S. Darwish 2020-09-08 11:41 ` peterz 2020-09-10 15:08 ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish 2020-09-04 15:32 ` [PATCH v2 3/5] seqlock: seqcount_t: Implement all read APIs as statement expressions Ahmed S. Darwish 2020-09-10 15:08 ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish 2020-09-04 15:32 ` [PATCH v2 4/5] seqlock: seqcount_LOCKNAME_t: Introduce PREEMPT_RT support Ahmed S. Darwish 2020-09-08 11:45 ` peterz 2020-09-08 12:48 ` Ahmed S. Darwish 2020-09-04 15:32 ` [PATCH v2 5/5] seqlock: PREEMPT_RT: Do not starve seqlock_t writers Ahmed S. Darwish 2020-09-10 15:08 ` [tip: locking/core] " tip-bot2 for Ahmed S. Darwish 2020-09-15 0:20 ` [PATCH v2 0/5] seqlock: Introduce PREEMPT_RT support Qian Cai 2020-09-15 12:48 ` Boqun Feng 2020-09-15 13:10 ` Boqun Feng 2020-09-15 14:30 ` peterz 2020-09-16 12:52 ` Qian Cai 2020-09-16 12:54 ` peterz 2020-09-16 13:00 ` Qian Cai 2020-09-16 13:02 ` peterz 2020-09-17 2:31 ` Stephen Rothwell 2020-09-18 8:42 ` [tip: locking/core] seqlock: Unbreak lockdep tip-bot2 for peterz@infradead.org
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