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SubjectRe: [PATCH] block: virtio_blk: don't hold spin lock during world switch
Date
Ming Lei <ming.lei@canonical.com> writes:
> 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
>
> fio script:
> [global]
> direct=1
> bsrange=4k-4k
> timeout=10
> numjobs=4
> ioengine=libaio
> iodepth=64
>
> filename=/dev/vdc
> group_reporting=1
>
> [f1]
> rw=randread
>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: virtualization@lists.linux-foundation.org
> Signed-off-by: Ming Lei <ming.lei@canonical.com>

Acked-by: Rusty Russell <rusty@rustcorp.com.au>

Thanks!
Rusty.


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