On 2014-05-29 20:49, Ming Lei wrote:
Firstly, it isn't necessary to hold lock of vblk->vq_lock when notifying hypervisor about queued I/O.Secondly, virtqueue_notify() will cause world switch and it may take long time on some hypervisors(such as, qemu-arm), so it isn't good to hold the lock and block other vCPUs. On arm64 quad core VM(qemu-kvm), the patch can increase I/O performance a lot with VIRTIO_RING_F_EVENT_IDX enabled: - without the patch: 14K IOPS - with the patch: 34K IOPS
Patch looks good to me. I don't see a hit on my qemu-kvm testing, but it definitely makes sense and I can see it hurting in other places.
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