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Date: Fri, 27 Jun 2014 09:35:47 +0200
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Subject: Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit
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To: Kevin Wolf <kwolf@redhat.com>
Cc: Ming Lei <tom.leiming@gmail.com>, Fam Zheng <famz@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

Il 27/06/2014 08:23, Kevin Wolf ha scritto:
> Note that there is already an interface in block.c that takes multiple
> requests at once, bdrv_aio_multiwrite(). It is currently used by
> virtio-blk, even though not in dataplane mode. It also submits
> individual requests to the block drivers currently, so effectively it
> doesn't make a difference, just the problem occurs in the block layer
> instead of the device.
>
> We should either improve bdrv_aio_multiwrite() to submit the requests in
> a batch to the block drivers, add a bdrv_aio_multiwrite() and use it for
> dataplane as well (possibly with a flag for disabling the request merging
> if we want to keep the current behaviour for dataplane); or, if we
> consider it a bad interface, replace it altogether with the new thing
> even for normal virtio-blk.

In fact, what's the status of Fam's patches to unify request processing 
between dataplane and non-dataplane?  They would add multiwrite support 
(also rerror/werror and blockstats).

I was hoping that they could get in 2.1.

Paolo

> If this makes a difference for dataplane, it probably makes a difference
> for all block devices.