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authorChristoph Hellwig <hch@lst.de>2009-09-04 22:44:42 +0200
committerRusty Russell <rusty@rustcorp.com.au>2009-10-22 16:39:26 +1030
commitf8b12e513b953aebf30f8ff7d2de9be7e024dbbe (patch)
treeec261949b674283b8ba214fd2715f3a7674da11c
parent2fdc246aaf9a7fa088451ad2a72e9119b5f7f029 (diff)
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 <hch@lst.de> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r--drivers/block/virtio_blk.c1
1 files changed, 0 insertions, 1 deletions
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 43f19389647..348befaaec7 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);