On 9/25/20 4:23 PM, Bjorn Helgaas wrote: > On Fri, Sep 25, 2020 at 02:26:54PM -0400, Nitesh Narayan Lal wrote: >> If we have isolated CPUs dedicated for use by real-time tasks, we try to >> move IRQs to housekeeping CPUs from the userspace to reduce latency >> overhead on the isolated CPUs. >> >> If we allocate too many IRQ vectors, moving them all to housekeeping CPUs >> may exceed per-CPU vector limits. >> >> When we have isolated CPUs, limit the number of vectors allocated by >> pci_alloc_irq_vectors() to the minimum number required by the driver, or >> to one per housekeeping CPU if that is larger. >> >> Signed-off-by: Nitesh Narayan Lal >> --- >> include/linux/pci.h | 17 +++++++++++++++++ >> 1 file changed, 17 insertions(+) >> >> diff --git a/include/linux/pci.h b/include/linux/pci.h >> index 835530605c0d..a7b10240b778 100644 >> --- a/include/linux/pci.h >> +++ b/include/linux/pci.h >> @@ -38,6 +38,7 @@ >> #include >> #include >> #include >> +#include >> #include >> >> #include >> @@ -1797,6 +1798,22 @@ static inline int >> pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs, >> unsigned int max_vecs, unsigned int flags) >> { >> + unsigned int hk_cpus; >> + >> + hk_cpus = housekeeping_num_online_cpus(HK_FLAG_MANAGED_IRQ); > Add blank line here before the block comment. > >> + /* >> + * If we have isolated CPUs for use by real-time tasks, to keep the >> + * latency overhead to a minimum, device-specific IRQ vectors are moved >> + * to the housekeeping CPUs from the userspace by changing their >> + * affinity mask. Limit the vector usage to keep housekeeping CPUs from >> + * running out of IRQ vectors. >> + */ >> + if (hk_cpus < num_online_cpus()) { >> + if (hk_cpus < min_vecs) >> + max_vecs = min_vecs; >> + else if (hk_cpus < max_vecs) >> + max_vecs = hk_cpus; >> + } > It seems like you'd want to do this inside > pci_alloc_irq_vectors_affinity() since that's an exported interface, > and drivers that use it will bypass the limiting you're doing here. Good point, few drivers directly use this. I took a quick look and it seems I may also have to take the pre and the post vectors into consideration. >> return pci_alloc_irq_vectors_affinity(dev, min_vecs, max_vecs, flags, >> NULL); >> } >> -- >> 2.18.2 >> -- Nitesh