From: Christoph Hellwig <hch@lst.de>
To: Asias He <asias@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Tejun Heo <tj@kernel.org>, Shaohua Li <shli@kernel.org>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH V5 4/4] virtio-blk: Add REQ_FLUSH and REQ_FUA support to bio path
Date: Thu, 2 Aug 2012 08:27:42 +0200 [thread overview]
Message-ID: <20120802062742.GA23573@lst.de> (raw)
In-Reply-To: <1343888757-25723-5-git-send-email-asias@redhat.com>
On Thu, Aug 02, 2012 at 02:25:56PM +0800, Asias He wrote:
> We need to support both REQ_FLUSH and REQ_FUA for bio based path since
> it does not get the sequencing of REQ_FUA into REQ_FLUSH that request
> based drivers can request.
>
> REQ_FLUSH is emulated by:
> 1. Send VIRTIO_BLK_T_FLUSH to device
> 2. Wait until the flush is finished
There is no need to wait for the flush to finish if the REQ_FLUSH
request has no data payload.
Even if it has a payload waiting is highly suboptimal and it should
use a non-blocking sequencing like it is done in the request layer.
>
> REQ_FUA is emulated by:
> 1. Send the actual write
> 2. Wait until the actual write is finished
> 3. Send VIRTIO_BLK_T_FLUSH to device
> 4. Wait until the flush is finished
> 5. Signal the end of the write to upper layer
The same comment about not blocking applies here as well.
next prev parent reply other threads:[~2012-08-02 6:27 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-02 6:25 [PATCH V5 0/4] Improve virtio-blk performance Asias He
2012-08-02 6:25 ` [PATCH V5 1/4] block: Introduce __blk_segment_map_sg() helper Asias He
2012-08-02 6:25 ` [PATCH V5 2/4] block: Add blk_bio_map_sg() helper Asias He
2012-08-02 6:25 ` [PATCH V5 3/4] virtio-blk: Add bio-based IO path for virtio-blk Asias He
2012-08-02 22:28 ` Michael S. Tsirkin
2012-08-03 7:11 ` Asias He
2012-08-02 6:25 ` [PATCH V5 4/4] virtio-blk: Add REQ_FLUSH and REQ_FUA support to bio path Asias He
2012-08-02 6:27 ` Christoph Hellwig [this message]
2012-08-02 6:43 ` Asias He
2012-08-06 15:17 ` Christoph Hellwig
2012-08-07 8:50 ` Asias He
2012-08-02 21:40 ` [PATCH V5 0/4] Improve virtio-blk performance Jens Axboe
2012-08-03 7:08 ` Asias He
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