linux-kernel - Re: [RFC v1 07/11] net/mlx4: Cache irq_desc->affinity instead of irq

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Message-ID: <alpine.DEB.2.11.1505041708190.4225@nanos>
Date:	Mon, 4 May 2015 17:10:26 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Amir Vadai <amirv@...lanox.com>
cc:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>, Ido Shamay <idos@...lanox.com>,
	"David S. Miller" <davem@...emloft.net>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Hadar Hen Zion <hadarh@...lanox.com>,
	Eran Ben Elisha <eranbe@...lanox.com>,
	Joe Perches <joe@...ches.com>,
	Saeed Mahameed <saeedm@...lanox.com>,
	Matan Barak <matanb@...lanox.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Tony Luck <tony.luck@...el.com>, x86@...nel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC v1 07/11] net/mlx4: Cache irq_desc->affinity instead of
 irq_desc

On Mon, 4 May 2015, Amir Vadai wrote:

> On Mon, May 4, 2015 at 6:15 AM, Jiang Liu <jiang.liu@...ux.intel.com> wrote:
> > The field 'affinity' in irq_desc won't change once the irq_desc data
> > structure is created. So cache irq_desc->affinity instead of irq_desc.
> > This also helps to hide struct irq_desc from device drivers.
> 
> Hi Jiang,
> 
> I might not understand the new changes irq core, but up until now
> affinity was changed when the user changed it through
> /proc/irq/<IRQ>/smp_affinity.
> This code is monitoring the affinity from the napi_poll context to
> detect affinity changes, and prevent napi from keep running on the
> wrong CPU.
> Therefore, the affinity can't be cached at the beginning. Please
> revert this caching.

Sigh. All of this is completely wrong. Polling in the internals of
irq_desc is just crap.

irq_set_affinity_notifier() has been added for exactly this purpose.

Please get rid of your irq_desc abuse.

Thanks,

	tglx


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