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@xxxxxxxxxx>
>> ---
>> 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
>>
--
Nitesh
Attachment:
signature.asc
Description: OpenPGP digital signature
