From: Marcelo Tosatti <mtosatti@redhat.com>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: linux-kernel@vger.kernel.org
Subject: [patch 2/2] nohz: try to avoid IPI when setting tick dependency for task
Date: Tue, 25 Aug 2020 15:41:49 -0300 [thread overview]
Message-ID: <20200825184414.486721471@fuller.cnet> (raw)
In-Reply-To: 20200825184147.948670309@fuller.cnet
When enabling per-CPU posix timers, an IPI to nohz_full CPUs might be
performed (to re-read the dependencies and possibly not re-enter
nohz_full on a given CPU).
A common case is for applications that run on nohz_full= CPUs
to not use POSIX timers (eg DPDK).
This patch optimizes tick_nohz_dep_set_task to avoid kicking
all nohz_full= CPUs in case the task allowed mask does not
intersect with nohz_full= CPU mask,
when going through tick_nohz_dep_set_task.
This reduces interruptions to nohz_full= CPUs.
---
kernel/time/tick-sched.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
Index: linux-2.6/kernel/time/tick-sched.c
===================================================================
--- linux-2.6.orig/kernel/time/tick-sched.c
+++ linux-2.6/kernel/time/tick-sched.c
@@ -383,11 +383,16 @@ void tick_nohz_dep_set_task(struct task_
tick_nohz_full_kick();
preempt_enable();
} else {
+ unsigned long flags;
+
/*
* Some future tick_nohz_full_kick_task()
- * should optimize this.
+ * should further optimize this.
*/
- tick_nohz_full_kick_all();
+ raw_spin_lock_irqsave(&tsk->pi_lock, flags);
+ if (cpumask_intersects(&tsk->cpus_mask, tick_nohz_full_mask))
+ tick_nohz_full_kick_all();
+ raw_spin_unlock_irqrestore(&tsk->pi_lock, flags);
}
}
}
next prev parent reply other threads:[~2020-08-25 18:46 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-25 18:41 [patch 0/2] posix-timers: avoid nohz_full= IPIs via task cpu masks Marcelo Tosatti
2020-08-25 18:41 ` [patch 1/2] nohz: try to avoid IPI when configuring per-CPU posix timer Marcelo Tosatti
2020-09-01 23:38 ` Frederic Weisbecker
2020-09-02 19:42 ` Marcelo Tosatti
2020-08-25 18:41 ` Marcelo Tosatti [this message]
2020-09-03 15:01 ` [patch 2/2] nohz: try to avoid IPI when setting tick dependency for task Frederic Weisbecker
2020-09-10 18:51 ` Marcelo Tosatti
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