linux-kernel - Re: [Ksummit-discuss] [TECH TOPIC] IRQ affinity

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Message-ID: <alpine.DEB.2.11.1507151408570.18576@nanos>
Date:	Wed, 15 Jul 2015 14:12:39 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Christoph Hellwig <hch@...radead.org>
cc:	ksummit-discuss@...ts.linuxfoundation.org,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-nvme@...ts.infradead.org
Subject: Re: [Ksummit-discuss] [TECH TOPIC] IRQ affinity

On Wed, 15 Jul 2015, Christoph Hellwig wrote:

> Many years ago we decided to move setting of IRQ to core affnities to
> userspace with the irqbalance daemon.
> 
> These days we have systems with lots of MSI-X vector, and we have
> hardware and subsystem support for per-CPU I/O queues in the block
> layer, the RDMA subsystem and probably the network stack (I'm not too
> familar with the recent developments there).  It would really help the
> out of the box performance and experience if we could allow such
> subsystems to bind interrupt vectors to the node that the queue is
> configured on.
> 
> I'd like to discuss if the rationale for moving the IRQ affinity setting
> fully to userspace are still correct in todays world any any pitfalls
> we'll have to learn from in irqbalanced and the old in-kernel affinity
> code.

I think setting an initial affinity is not going to create the horror
of the old in-kernel irq balancer again. It still could be changed
from user space and does not try to be smart by moving interrupts
around in circles all the time.

Thanks,

	tglx


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