Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2

[Paolo Bonzini <pbonzini@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.