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Thu, 29 May 2025 23:07:40 -0700 (PDT) Received: from localhost.localdomain ([39.144.44.150]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-747affcf9ffsm2365083b3a.135.2025.05.29.23.07.32 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 29 May 2025 23:07:39 -0700 (PDT) From: Yafang Shao To: mingo@redhat.com, peterz@infradead.org, mkoutny@suse.com, hannes@cmpxchg.org Cc: juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, surenb@google.com, linux-kernel@vger.kernel.org, Yafang Shao , Eric Dumazet Subject: [PATCH] sched: Annotate sched_clock_irqtime with __read_mostly Date: Fri, 30 May 2025 14:07:26 +0800 Message-Id: <20250530060726.67380-1-laoar.shao@gmail.com> X-Mailer: git-send-email 2.37.1 (Apple Git-137.1) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Eric reported an issue [0] as follows, : rebalance_domains() can attempt to change sched_balance_running : more than 350,000 times per second on our servers. : If sched_clock_irqtime and sched_balance_running share the : same cache line, we see a very high cost on hosts with 480 threads : dealing with many interrupts. While the rebalance_domains() issue has been resolved [1], we should proactively annotate sched_clock_irqtime with __read_mostly to prevent potential cacheline false sharing. This optimization is particularly justified since sched_clock_irqtime is only modified during TSC instability events. Link: https://lore.kernel.org/all/20250423174634.3009657-1-edumazet@google.= com/ [0] Link: https://lore.kernel.org/all/20250416035823.1846307-1-tim.c.chen@linux= .intel.com/ [1] Reported-by: Eric Dumazet Debugged-by: Eric Dumazet Signed-off-by: Yafang Shao Reviewed-by: Michal Koutn=C3=BD Cc: Eric Dumazet --- kernel/sched/cputime.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 6dab4854c6c0..c499a42ceda4 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -22,7 +22,7 @@ */ DEFINE_PER_CPU(struct irqtime, cpu_irqtime); =20 -int sched_clock_irqtime; +int __read_mostly sched_clock_irqtime; =20 void enable_sched_clock_irqtime(void) { --=20 2.43.5