From: Arthur Kepner <akepner@sgi.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org
Subject: Re: [RFC/PATCHv2] x86/irq: round-robin distribution of irqs to cpus w/in node
Date: Mon, 27 Sep 2010 15:01:13 -0700 [thread overview]
Message-ID: <20100927220113.GD30050@sgi.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1009272236430.2416@localhost6.localdomain6>
On Mon, Sep 27, 2010 at 10:46:02PM +0200, Thomas Gleixner wrote:
> ...
> Sigh. Why is this a x86 specific problem ?
>
It's obviously not. But we're particularly seeing it on x86
systems, so an x86-specific fix would address our problem.
> If we setup an irq on a node then we should set the affinity to the
> target node in general.
OK.
> .... The round robin inside the node is really not
> a problem unless you hit:
>
> nr_irqs_per_node * nr_cpus_per_node > max_vectors_per_cpu
>
No, I don't think that's true.
The problem we're seeing is that one driver asks for a large
number of interrupts (on no CPU in particular). And because of the
way that the vectors are initially assigned to CPUs (in
__assign_irq_vector()), a particular CPU can have all its vectors
consumed.
Now, a second driver comes along, and requests an interrupt on
a specific CPU, N. But CPU N is out of interrupts, so that driver
fails.
This all happens before a user-space irq balancer is available.
--
Arthur
next prev parent reply other threads:[~2010-09-27 22:01 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-27 20:34 [RFC/PATCHv2] x86/irq: round-robin distribution of irqs to cpus w/in node Arthur Kepner
2010-09-27 20:46 ` Thomas Gleixner
2010-09-27 22:01 ` Arthur Kepner [this message]
2010-09-27 22:12 ` Thomas Gleixner
2010-09-28 0:17 ` Eric W. Biederman
2010-09-28 8:08 ` Thomas Gleixner
2010-09-28 10:59 ` Eric W. Biederman
2010-09-29 17:19 ` Arthur Kepner
2010-09-29 18:05 ` Thomas Gleixner
2010-10-17 10:44 ` Thomas Gleixner
2010-10-19 23:58 ` Arthur Kepner
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