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From: Chris Friesen <chris.friesen@windriver.com>
To: linux-pci@vger.kernel.org
Subject: PCI, isolcpus, and irq affinity
Date: Mon, 12 Oct 2020 09:49:37 -0600	[thread overview]
Message-ID: <83d03f27-d92d-1b28-ad28-cbe5d011fe33@windriver.com> (raw)

Hi,

I'm not subscribed to the list so please CC me on replies.

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).

Looking at the code, it appears that the NVME driver can in some 
scenarios end up calling pci_alloc_irq_vectors_affinity() after initial 
system startup, which seems to determine CPU affinity without any regard 
for things like "isolcpus" or "cset shield".

There seem to be other reports of similar issues:

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1831566

It looks like some SCSI drivers and virtio_pci_common.c will also call 
pci_alloc_irq_vectors_affinity(), though I'm not sure if they would ever 
do it after system startup.

How does it make sense for the PCI subsystem to affine interrupts to 
CPUs which have explicitly been designated as "isolated"?

Thanks,

Chris



             reply	other threads:[~2020-10-12 15:49 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-12 15:49 Chris Friesen [this message]
2020-10-12 16:58 ` PCI, isolcpus, and irq affinity 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
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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