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

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Date:	Mon, 04 May 2015 22:00:38 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Amir Vadai <amirv@...lanox.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	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 2015/5/4 20:10, 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.
Hi Amir,
	Thanks for review:) We want to hide irq_desc implementation
details from device drivers, so made these changes.
	Function irq_get_affinity_mask() returns 'struct cpumask *'
and we cache the returned pointer. On the other hand, user may change
IRQ affinity through /proc/irq/<IRQ>/smp_affinity, but that only
changes the bitmap pointed to by the cached pointer and won't change
the pointer itself. So it should always return the latest affinity
setting by calling cpumask_test_cpu(cpu_curr, cq->irq_affinity).
Or am I missing something here?
Thanks!
Gerry
> 
> Thanks,
> Amir
> 
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