On Fri, May 30, 2014 at 11:19 AM, Jens Axboe <ax...@kernel.dk> wrote: > 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.
It isn't easy to observe the improvement on x86 VM, especially with few vCPUs, because qemu-system-x86_64 only takes several microseconds to handle the notification, but on arm64, it may take hundreds of microseconds, so the improvement is obvious on arm VM. I hope this patch can be merged, at least arm VM can benefit from it. Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
