From: Thomas Gleixner <email@example.com> To: Bjorn Helgaas <firstname.lastname@example.org>, Chris Friesen <email@example.com> Cc: firstname.lastname@example.org, Christoph Hellwig <email@example.com>, Nitesh Narayan Lal <firstname.lastname@example.org> Subject: Re: PCI, isolcpus, and irq affinity Date: Mon, 12 Oct 2020 19:50:04 +0200 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <20201012165839.GA3732859@bjorn-Precision-5520> 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. > pci_alloc_irq_vectors_affinity() basically just passes affinity > information through to kernel/irq/affinity.c, and the PCI core doesn't > change affinity after that. Correct. > This recent thread may be useful: > > https://firstname.lastname@example.org/ > > It contains a patch to "Limit pci_alloc_irq_vectors() to housekeeping > CPUs". I'm not sure that patch summary is 100% accurate because IIUC > that particular patch only reduces the *number* of vectors allocated > and does not actually *limit* them to housekeeping CPUs. That patch is a bandaid at best and for the managed interrupt scenario not really preventing that interrupts + threads are affine to isolated CPUs. Thanks, tglx
next prev parent reply other threads:[~2020-10-12 17:50 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 [this message] 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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