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From: Thomas Gleixner <tglx@linutronix.de>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@infradead.org>,
	linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
	Laurence Oberman <loberman@redhat.com>
Subject: Re: [PATCH V3 4/4] genirq/affinity: irq vector spread among online CPUs as far as possible
Date: Thu, 5 Apr 2018 12:12:24 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1804051206050.2204@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20180404152018.GB24824@ming.t460p>

On Wed, 4 Apr 2018, Ming Lei wrote:
> On Wed, Apr 04, 2018 at 02:45:18PM +0200, Thomas Gleixner wrote:
> > Now the 4 offline CPUs are plugged in again. These CPUs won't ever get an
> > interrupt as all interrupts stay on CPU 0-3 unless one of these CPUs is
> > unplugged. Using cpu_present_mask the spread would be:
> > 
> >  	irq 39, cpu list 0,1
> >  	irq 40, cpu list 2,3
> >  	irq 41, cpu list 4,5
> >  	irq 42, cpu list 6,7
> 
> Given physical CPU hotplug isn't common, this way will make only irq 39
> and irq 40 active most of times, so performance regression is caused just
> as Kashyap reported.

That is only true, if CPU 4-7 are in the present mask at boot time. I
seriously doubt that this is the case for Kashyaps scenario. Grrr, if you
would have included him into the Reported-by: tags then I could have asked
him myself.

In the physical hotplug case, the physcially (or virtually) not available
CPUs are not in the present mask. They are solely in the possible mask.

The above is about soft hotplug where the CPUs are physically there and
therefore in the present mask and can be onlined without interaction from
the outside (mechanical or virt config).

If nobody objects, I'll make that change and queue the stuff tomorrow
morning so it can brew a few days in next before I send it off to Linus.

Thanks,

	tglx

  reply	other threads:[~2018-04-05 10:12 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-08 10:53 [PATCH V3 0/4] genirq/affinity: irq vector spread among online CPUs as far as possible Ming Lei
2018-03-08 10:53 ` [PATCH V3 1/4] genirq/affinity: rename *node_to_possible_cpumask as *node_to_cpumask Ming Lei
2018-04-06 21:52   ` [tip:irq/core] genirq/affinity: Rename " tip-bot for Ming Lei
2018-03-08 10:53 ` [PATCH V3 2/4] genirq/affinity: move actual irq vector spread into one helper Ming Lei
2018-04-06 21:53   ` [tip:irq/core] genirq/affinity: Move actual irq vector spreading into a helper function tip-bot for Ming Lei
2018-03-08 10:53 ` [PATCH V3 3/4] genirq/affinity: support to do irq vectors spread starting from any vector Ming Lei
2018-04-06 21:53   ` [tip:irq/core] genirq/affinity: Allow irq spreading from a given starting point tip-bot for Ming Lei
2018-03-08 10:53 ` [PATCH V3 4/4] genirq/affinity: irq vector spread among online CPUs as far as possible Ming Lei
2018-04-03 13:32   ` Thomas Gleixner
2018-04-03 16:00     ` Ming Lei
2018-04-04  8:25       ` Thomas Gleixner
2018-04-04 12:45         ` Thomas Gleixner
2018-04-04 15:20           ` Ming Lei
2018-04-05 10:12             ` Thomas Gleixner [this message]
2018-04-04 15:08         ` Ming Lei
2018-04-04 19:38           ` Thomas Gleixner
2018-04-06  9:13             ` Ming Lei
2018-04-06  9:46               ` Thomas Gleixner
2018-04-06 21:49                 ` Thomas Gleixner
2018-04-08  3:19                   ` Ming Lei
2018-04-06 21:54   ` [tip:irq/core] genirq/affinity: Spread irq vectors among present " tip-bot for Ming Lei
2018-03-08 13:18 ` [PATCH V3 0/4] genirq/affinity: irq vector spread among online " Artem Bityutskiy
2018-03-08 13:25   ` Artem Bityutskiy
2018-03-08 13:34   ` Ming Lei
2018-03-08 23:20     ` Thomas Gleixner
2018-03-09  1:24       ` Ming Lei
2018-03-09  7:00         ` Artem Bityutskiy
2018-03-09  7:33           ` Ming Lei
2018-03-09 10:08         ` Thomas Gleixner
2018-03-09 12:08           ` Ming Lei
2018-03-09 15:08             ` Thomas Gleixner
2018-03-13  3:11               ` Dou Liyang
2018-03-13  7:38                 ` Artem Bityutskiy
2018-03-13  7:38                   ` Artem Bityutskiy
2018-03-13  8:35                   ` Ming Lei
2018-03-13  8:39                     ` Artem Bityutskiy
2018-03-13  8:39                       ` Artem Bityutskiy
2018-03-13  9:35                       ` Rafael J. Wysocki
2018-03-14  3:29                         ` Dou Liyang
2018-03-14  4:11                           ` Dou Liyang
2018-03-14  9:07                             ` Artem Bityutskiy
2018-03-14  9:47                               ` Dou Liyang
2018-03-13  9:25                 ` Rafael J. Wysocki
2018-03-14  3:30                   ` Dou Liyang
2018-03-30  3:15               ` Ming Lei
2018-04-03 12:55                 ` Thomas Gleixner
2018-03-26  8:39   ` Thorsten Leemhuis
2018-03-28  6:15     ` Artem Bityutskiy

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