| Message ID | 20200925182654.224004-5-nitesh@redhat.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | isolation: limit msix vectors to housekeeping CPUs | expand |
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 <nitesh@redhat.com> > --- > 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 <linux/interrupt.h> > #include <linux/io.h> > #include <linux/resource_ext.h> > +#include <linux/sched/isolation.h> > #include <uapi/linux/pci.h> > > #include <linux/pci_ids.h> > @@ -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. > return pci_alloc_irq_vectors_affinity(dev, min_vecs, max_vecs, flags, > NULL); > } > -- > 2.18.2 >
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 <nitesh@redhat.com> >> --- >> 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 <linux/interrupt.h> >> #include <linux/io.h> >> #include <linux/resource_ext.h> >> +#include <linux/sched/isolation.h> >> #include <uapi/linux/pci.h> >> >> #include <linux/pci_ids.h> >> @@ -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 >>
On 9/25/20 5:38 PM, Nitesh Narayan Lal wrote: > On 9/25/20 4:23 PM, Bjorn Helgaas wrote: [...] >>> + /* >>> + * 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. > It seems my initial interpretation was incorrect, reserved vecs (pre+post) should always be less than the min_vecs. So, FWIU we should be fine in limiting the max_vecs. I can make this change and do a repost. Do you have any other concerns with this patch or with any of the other patches? [...]
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 <linux/interrupt.h> #include <linux/io.h> #include <linux/resource_ext.h> +#include <linux/sched/isolation.h> #include <uapi/linux/pci.h> #include <linux/pci_ids.h> @@ -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); + /* + * 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; + } return pci_alloc_irq_vectors_affinity(dev, min_vecs, max_vecs, flags, NULL); }
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 <nitesh@redhat.com> --- include/linux/pci.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)