From: Scott Wood <swood@redhat.com>
To: Waiman Long <longman@redhat.com>,
linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Juri Lelli <jlelli@redhat.com>
Subject: Re: [PATCH RT] kernel/sched: Don't recompute cpumask weight in migrate_enable_update_cpus_allowed()
Date: Sat, 12 Oct 2019 02:06:16 -0500 [thread overview]
Message-ID: <0979a9a345e47be69783a2183dd31911e9fc755e.camel@redhat.com> (raw)
In-Reply-To: <20191011140908.5161-1-longman@redhat.com>
On Fri, 2019-10-11 at 10:09 -0400, Waiman Long wrote:
> At each invocation of rt_spin_unlock(), cpumask_weight() is called
> via migrate_enable_update_cpus_allowed() to recompute the weight of
> cpus_mask which doesn't change that often.
>
> The following is a sample output of perf-record running the testpmd
> microbenchmark on an RT kernel:
>
> 34.77% 1.65% testpmd [kernel.kallsyms] [k] rt_spin_unlock
> 34.32% 2.52% testpmd [kernel.kallsyms] [k] migrate_enable
> 21.76% 21.76% testpmd [kernel.kallsyms] [k] __bitmap_weight
>
> By adding an extra variable to keep track of the weight of cpus_mask,
> we could eliminate the frequent call to cpumask_weight() and replace
> it with simple assignment.
Can you try this with my migrate disable patchset (which makes
amigrate_enable_update_cpus_allowed() be called much less often) and see if
caching nr_cpus_allowed still makes a difference?
-Scott
next prev parent reply other threads:[~2019-10-12 7:06 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-11 14:09 [PATCH RT] kernel/sched: Don't recompute cpumask weight in migrate_enable_update_cpus_allowed() Waiman Long
2019-10-12 7:06 ` Scott Wood [this message]
2019-10-18 18:18 ` Waiman Long
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