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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43fe4e3a381sm17044529f8f.21.2026.04.18.13.42.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 18 Apr 2026 13:42:38 -0700 (PDT) From: David Carlier To: Johannes Weiner , Peter Zijlstra , Ingo Molnar Cc: Suren Baghdasaryan , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , linux-kernel@vger.kernel.org, David Carlier Subject: [PATCH] sched/psi: Use try_cmpxchg() helpers in event and rtpoll wakeup paths Date: Sat, 18 Apr 2026 21:42:35 +0100 Message-ID: <20260418204235.9957-1-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In update_triggers(), the event-generation gate uses cmpxchg(&t->event, 0, 1) == 0 to detect a 0 -> 1 transition. On x86 this compiles to CMPXCHG followed by a redundant compare of the returned value against the expected. try_cmpxchg() avoids the extra compare by reading ZF directly from CMPXCHG. Convert the call site to the try_cmpxchg() form, using a per-iteration comparand local so the failure-path writeback does not leak across loop iterations. In psi_rtpoll_worker(), the wait_event_interruptible() condition uses atomic_cmpxchg(&group->rtpoll_wakeup, 1, 0) as a test-and-clear of the wakeup flag. An inline conversion is unsafe: try_cmpxchg() writes the observed value back into the expected-value lvalue on failure, and wait_event_interruptible() re-evaluates the condition many times per call, which would cause the comparand to drift and wakeups to be lost. Factor the test-and-clear into psi_rtpoll_consume_wakeup(), which materializes a fresh comparand per invocation, and call it from the wait_event_interruptible() condition. Use the fully ordered atomic_try_cmpxchg() to preserve the original memory ordering. No functional change. Assisted-by: Claude:claude-opus-4-7 [tool claude-code] Signed-off-by: David Carlier --- kernel/sched/psi.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index d9c9d9480a45..868833bca4d4 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -482,6 +482,7 @@ static void update_triggers(struct psi_group *group, u64 now, */ list_for_each_entry(t, triggers, node) { u64 growth; + int zero = 0; bool new_stall; new_stall = aggregator_total[t->state] != total[t->state]; @@ -510,7 +511,7 @@ static void update_triggers(struct psi_group *group, u64 now, continue; /* Generate an event */ - if (cmpxchg(&t->event, 0, 1) == 0) { + if (try_cmpxchg(&t->event, &zero, 1)) { if (t->of) kernfs_notify(t->of->kn); else @@ -735,6 +736,12 @@ static void psi_rtpoll_work(struct psi_group *group) mutex_unlock(&group->rtpoll_trigger_lock); } +static bool psi_rtpoll_consume_wakeup(struct psi_group *group) +{ + int wakeup = 1; + return atomic_try_cmpxchg(&group->rtpoll_wakeup, &wakeup, 0); +} + static int psi_rtpoll_worker(void *data) { struct psi_group *group = (struct psi_group *)data; @@ -743,7 +750,7 @@ static int psi_rtpoll_worker(void *data) while (true) { wait_event_interruptible(group->rtpoll_wait, - atomic_cmpxchg(&group->rtpoll_wakeup, 1, 0) || + psi_rtpoll_consume_wakeup(group) || kthread_should_stop()); if (kthread_should_stop()) break; -- 2.53.0