On Wed, May 27, 2020 at 11:38:17AM +0100, Daniel P. Berrangé wrote: > On Wed, May 27, 2020 at 11:29:23AM +0100, Stefan Hajnoczi wrote: > > Automatically size the number of virtio-scsi-pci, vhost-scsi-pci, and > > vhost-user-scsi-pci request virtqueues to match the number of vCPUs. > > Other transports continue to default to 1 request virtqueue. > > IIRC this was raised on earlier versions of the series, but i don't > recall the outcome and no caveats are mentioned here... > > Is this default still valid for very large $vCPUs. eg if I run QEMU > with "-smp 512" or even larger (I've seen people discussing 1000's of > CPUs), is this going to cause problems with the virtio-scsi default > queue counts ? Is there such a thing as "too large" for the num > of queues setting ? num vectors defaults to a value derived from > num queues, so is there concept of "too large" for num of vectors > setting ? > > Ideally the commit message would answer these questions for future > reference. Same for the next patch to virtio-blk
Good point. Actually this patch and the virtio-blk ones no longer contain the queue number policy. The new virtio_pci_optimal_num_queues() function encapsulates the policy to avoid duplication. I'll resend and update that patch with the full rationale. Thanks!
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