From f8b12e513b953aebf30f8ff7d2de9be7e024dbbe Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Fri, 4 Sep 2009 22:44:42 +0200 Subject: virtio_blk: revert QUEUE_FLAG_VIRT addition It seems like the addition of QUEUE_FLAG_VIRT caueses major performance regressions for Fedora users: https://bugzilla.redhat.com/show_bug.cgi?id=509383 https://bugzilla.redhat.com/show_bug.cgi?id=505695 while I can't reproduce those extreme regressions myself I think the flag is wrong. Rationale: QUEUE_FLAG_VIRT expands to QUEUE_FLAG_NONROT which casus the queue unplugged immediately. This is not a good behaviour for at least qemu and kvm where we do have significant overhead for every I/O operations. Even with all the latested speeups (native AIO, MSI support, zero copy) we can only get native speed for up to 128kb I/O requests we already are down to 66% of native performance for 4kb requests even on my laptop running the Intel X25-M SSD for which the QUEUE_FLAG_NONROT was designed. If we ever get virtio-blk overhead low enough that this flag makes sense it should only be set based on a feature flag set by the host. Signed-off-by: Christoph Hellwig Signed-off-by: Rusty Russell --- drivers/block/virtio_blk.c | 1 - 1 file changed, 1 deletion(-) (limited to 'drivers/block') diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 43f19389647a..348befaaec73 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -332,7 +332,6 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) } vblk->disk->queue->queuedata = vblk; - queue_flag_set_unlocked(QUEUE_FLAG_VIRT, vblk->disk->queue); if (index < 26) { sprintf(vblk->disk->disk_name, "vd%c", 'a' + index % 26); -- cgit v1.2.3