From: Asias He <asias@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH V3 3/3] virtio-blk: Add bio-based IO path for virtio-blk
Date: Mon, 30 Jul 2012 12:43:12 +0800 [thread overview]
Message-ID: <501610E0.8000504@redhat.com> (raw)
In-Reply-To: <971756309.4742543.1343457753475.JavaMail.root@redhat.com>
On 07/28/2012 02:42 PM, Paolo Bonzini wrote:
>>> I'm not sure what the correct behavior for bio & cacheflush is, if
>>> any.
>>
>> REQ_FLUSH is not supported in the bio path.
>
> Ouch, that's correct:
>
> @@ -414,7 +529,7 @@ static void virtblk_update_cache_mode(struct virtio_device *vdev)
> u8 writeback = virtblk_get_cache_mode(vdev);
> struct virtio_blk *vblk = vdev->priv;
>
> - if (writeback)
> + if (writeback && !use_bio)
> blk_queue_flush(vblk->disk->queue, REQ_FLUSH);
> else
> blk_queue_flush(vblk->disk->queue, 0);
>
> then it is not safe against power losses.
Yes. Something like this:
qemu -drive file=foo.img,cache=writeback/unsafe
is not safe against power losses also?
I think we can add REQ_FLUSH & REQ_FUA support to bio path and that
deserves another patch.
--
Asias
next prev parent reply other threads:[~2012-07-30 4:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-13 8:38 [PATCH V3 0/3] Improve virtio-blk performance Asias He
2012-07-13 8:38 ` [PATCH V3 1/3] block: Introduce __blk_segment_map_sg() helper Asias He
2012-07-13 8:38 ` [PATCH V3 2/3] block: Add blk_bio_map_sg() helper Asias He
2012-07-13 8:38 ` [PATCH V3 3/3] virtio-blk: Add bio-based IO path for virtio-blk Asias He
2012-07-27 0:33 ` Rusty Russell
2012-07-28 2:38 ` Asias He
2012-07-28 6:42 ` Paolo Bonzini
2012-07-30 4:43 ` Asias He [this message]
2012-07-30 7:31 ` Paolo Bonzini
2012-07-30 13:44 ` Christoph Hellwig
2012-08-02 6:28 ` Asias He
2012-07-30 13:43 ` Christoph Hellwig
2012-07-31 8:43 ` Asias He
2012-07-29 12:59 ` Michael S. Tsirkin
2012-07-30 0:26 ` Asias He
2012-07-27 6:29 ` Rusty Russell
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