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://lore.kernel.org/linux-pci/20200928183529.471328-1-nitesh@xxxxxxxxxx/ > > 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
