• M
    block: virtio_blk: don't hold spin lock during world switch · e8edca6f
    Ming Lei 提交于
    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: NMing Lei <ming.lei@canonical.com>
    Acked-by: NRusty Russell <rusty@rustcorp.com.au>
    Cc: stable@kernel.org # 3.13+
    Signed-off-by: NJens Axboe <axboe@fb.com>
    e8edca6f
virtio_blk.c 21.1 KB