On Fri, Jul 27, 2012 at 04:38:11PM +0200, Paolo Bonzini wrote: > Il 05/07/2012 12:29, Jason Wang ha scritto: > > Sometimes, virtio device need to configure irq affiniry hint to maximize the > > performance. Instead of just exposing the irq of a virtqueue, this patch > > introduce an API to set the affinity for a virtqueue. > > > > The api is best-effort, the affinity hint may not be set as expected due to > > platform support, irq sharing or irq type. Currently, only pci method were > > implemented and we set the affinity according to: > > > > - if device uses INTX, we just ignore the request > > - if device has per vq vector, we force the affinity hint > > - if the virtqueues share MSI, make the affinity OR over all affinities > > requested > > > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> > > Hmm, I don't see any benefit from this patch, I need to use > irq_set_affinity (which however is not exported) to actually bind IRQs > to CPUs. Example: > > with irq_set_affinity_hint: > 43: 89 107 100 97 PCI-MSI-edge virtio0-request > 44: 178 195 268 199 PCI-MSI-edge virtio0-request > 45: 97 100 97 155 PCI-MSI-edge virtio0-request > 46: 234 261 213 218 PCI-MSI-edge virtio0-request > > with irq_set_affinity: > 43: 721 0 0 1 PCI-MSI-edge virtio0-request > 44: 0 746 0 1 PCI-MSI-edge virtio0-request > 45: 0 0 658 0 PCI-MSI-edge virtio0-request > 46: 0 0 1 547 PCI-MSI-edge virtio0-request > > I gathered these quickly after boot, but real benchmarks show the same > behavior, and performance gets actually worse with virtio-scsi > multiqueue+irq_set_affinity_hint than with irq_set_affinity. > > I also tried adding IRQ_NO_BALANCING, but the only effect is that I > cannot set the affinity > > The queue steering algorithm I use in virtio-scsi is extremely simple > and based on your tx code. See how my nice pinning is destroyed: > > # taskset -c 0 dd if=/dev/sda bs=1M count=1000 of=/dev/null iflag=direct > # cat /proc/interrupts > 43: 2690 2709 2691 2696 PCI-MSI-edge virtio0-request > 44: 109 122 199 124 PCI-MSI-edge virtio0-request > 45: 170 183 170 237 PCI-MSI-edge virtio0-request > 46: 143 166 125 125 PCI-MSI-edge virtio0-request > > All my requests come from CPU#0 and thus go to the first virtqueue, but > the interrupts are serviced all over the place. > > Did you set the affinity manually in your experiments, or perhaps there > is a difference between scsi and networking... (interrupt mitigation?) > > Paolo You need to run irqbalancer in guest to make it actually work. Do you? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
