On Wed, Feb 8, 2017 at 11:37 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > IIRC irqbalance will bail out and avoid touching affinity > if you set affinity from driver. Breaking that's not nice. > Pls correct me if I'm wrong. I believe you're right that irqbalance will leave the affinity alone. Irqbalance has had changes that may or may not be in the versions bundled with various guests, and I don't have a definitive cross-correlation of irqbalance version to guest version. But in the existing code, the driver does set affinity for #VCPUs==#queues, so that's been happening anyway. The (original) intention of this patch was to extend the existing behavior to the case where we limit queue counts, to avoid the surprising discontinuity when #VCPU != #queues. It's not obvious that it's wrong to cause irqbalance to leave these queues alone: Generally you want the interrupt to come to the core that caused the work, to have cache locality and avoid lock contention. Doing fancier things is outside the scope of this patch. > Doesn't look like this will handle the case of num cpus < num queues well. I believe it's correct. The first #VCPUs queues will have one bit set in their xps mask, and the remaining queues have no bits set. That means each VCPU uses its own assigned TX queue (and the TX interrupt comes back to that VCPU). Thanks again for the review! Ben -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
