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From: Chris Friesen <chris.friesen@windriver.com>
To: Thomas Gleixner <tglx@linutronix.de>, Bjorn Helgaas <helgaas@kernel.org>
Cc: linux-pci@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
	Nitesh Narayan Lal <nitesh@redhat.com>
Subject: Re: PCI, isolcpus, and irq affinity
Date: Mon, 12 Oct 2020 12:58:41 -0600	[thread overview]
Message-ID: <df1be4be-88b5-b848-97bf-4c38824e840a@windriver.com> (raw)
In-Reply-To: <87a6wrqqpf.fsf@nanos.tec.linutronix.de>

On 10/12/2020 11:50 AM, Thomas Gleixner wrote:
> On Mon, Oct 12 2020 at 11:58, Bjorn Helgaas wrote:
>> On Mon, Oct 12, 2020 at 09:49:37AM -0600, Chris Friesen wrote:
>>> I've got a linux system running the RT kernel with threaded irqs.  On
>>> startup we affine the various irq threads to the housekeeping CPUs, but I
>>> recently hit a scenario where after some days of uptime we ended up with a
>>> number of NVME irq threads affined to application cores instead (not good
>>> when we're trying to run low-latency applications).
> 
> These threads and the associated interupt vectors are completely
> harmless and fully idle as long as there is nothing on those isolated
> CPUs which does disk I/O.

Some of the irq threads are affined (by the kernel presumably) to 
multiple CPUs (nvme1q2 and nvme0q2 were both affined 0x38000038, a 
couple of other queues were affined 0x1c00001c0).

In this case could disk I/O submitted by one of those CPUs end up 
interrupting another one?

Chris

  reply	other threads:[~2020-10-12 18:58 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-12 15:49 Chris Friesen
2020-10-12 16:58 ` Bjorn Helgaas
2020-10-12 17:39   ` Sean V Kelley
2020-10-12 19:18     ` Chris Friesen
2020-10-12 17:42   ` Nitesh Narayan Lal
2020-10-12 17:50   ` Thomas Gleixner
2020-10-12 18:58     ` Chris Friesen [this message]
2020-10-12 19:07       ` Keith Busch
2020-10-12 19:44         ` Thomas Gleixner
2020-10-15 18:47         ` Chris Friesen
2020-10-15 19:02           ` Keith Busch
2020-10-12 19:31       ` Thomas Gleixner
2020-10-12 20:24         ` David Woodhouse
2020-10-12 22:25           ` Thomas Gleixner

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