From: Thomas Gleixner <tglx@linutronix.de>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
Nadav Amit <namit@vmware.com>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH V2] cpu/hotplug: Cache number of online CPUs
Date: Mon, 8 Jul 2019 16:20:09 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1907081618270.4709@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20190708140732.GI26519@linux.ibm.com>
On Mon, 8 Jul 2019, Paul E. McKenney wrote:
> On Mon, Jul 08, 2019 at 03:43:55PM +0200, Thomas Gleixner wrote:
> > Revaluating the bitmap wheight of the online cpus bitmap in every
>
> s/wheight/weight/?
>
> > invocation of num_online_cpus() over and over is a pretty useless
> > exercise. Especially when num_online_cpus() is used in code pathes like the
> > IPI delivery of x86 or the membarrier code.
> >
> > Cache the number of online CPUs in the core and just return the cached
> > variable.
>
> I do like this and the comments on limited guarantees make sense.
> One suggestion for saving a few lines below, but either way:
Nah. I have to redo it. Mathieu just pointed out in IRC that there is the
reboot and emergency/panic/kexec crap which calls set_cpu_online()
completely non serialized. Sigh....
Thanks,
tglx
next prev parent reply other threads:[~2019-07-08 14:20 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-04 20:42 [PATCH] cpu/hotplug: Cache number of online CPUs Thomas Gleixner
2019-07-04 20:59 ` Mathieu Desnoyers
2019-07-04 21:10 ` Thomas Gleixner
2019-07-04 22:00 ` Mathieu Desnoyers
2019-07-04 22:33 ` Thomas Gleixner
2019-07-04 23:34 ` Mathieu Desnoyers
2019-07-05 8:49 ` Ingo Molnar
2019-07-05 15:38 ` Mathieu Desnoyers
2019-07-05 20:53 ` Thomas Gleixner
2019-07-05 21:00 ` Thomas Gleixner
2019-07-06 23:24 ` Mathieu Desnoyers
2019-07-08 13:43 ` [PATCH V2] " Thomas Gleixner
2019-07-08 14:07 ` Paul E. McKenney
2019-07-08 14:20 ` Thomas Gleixner [this message]
2019-07-09 14:23 ` [PATCH V3] " Thomas Gleixner
2019-07-09 15:52 ` Mathieu Desnoyers
2019-07-22 7:58 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2019-07-25 14:11 ` tip-bot for Thomas Gleixner
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