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Date: Tue, 28 Apr 2015 16:03:37 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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In-Reply-To: <20150428152054.3a84658c.cornelia.huck@de.ibm.com>
Subject: Re: [Qemu-devel] [PATCH v4 0/2] virtio: Move host features to
	backends
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To: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, hangaohuai@huawei.com, "Huangpeng (Peter)" <peter.huangpeng@huawei.com>, QEMU Developers <qemu-devel@nongnu.org>, Shannon Zhao <shannon.zhao@linaro.org>, Shannon Zhao <zhaoshenglong@huawei.com>, Paolo Bonzini <pbonzini@redhat.com>, Christoffer Dall <christoffer.dall@linaro.org>

On Tue, Apr 28, 2015 at 03:20:54PM +0200, Cornelia Huck wrote:
> On Tue, 28 Apr 2015 15:05:47 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Tue, Apr 28, 2015 at 01:52:40PM +0100, Peter Maydell wrote:
> > > On 28 April 2015 at 13:48, Michael S. Tsirkin <mst@redhat.com> wrote:
> > > > On Tue, Apr 28, 2015 at 07:51:11PM +0800, shannon.zhao@linaro.org wrote:
> > > >> From: Shannon Zhao <shannon.zhao@linaro.org>
> > > >> Here we move the host features to backends, involving
> > > >> DEFINE_VIRTIO_NET_FEATURES, DEFINE_VIRTIO_SCSI_FEATURES. So the
> > > >> virtio-mmio devices could have the host freatures, and this has a great
> > > >> performance improvement to virtio-mmio, especially to virtio-net-device.
> > > >
> > > > Can you move COMMON_FEATURES too please?
> > > 
> > > I think that would be wrong -- COMMON_FEATURES are transport features,
> > > not backend-specific features, so they belong on the transports
> > > (and on the convenience wrappers), not the backends.
> > > 
> > > thanks
> > > -- PMM
> > 
> > Hmm you are right. The problem is with s390 which
> > puts this DEFINE_VIRTIO_COMMON_FEATURES in all devices.
> 
> All save virtio-blk. There were some problems when switching on
> event_idx on virtio-blk, IIRC.

Specifically on s390?

> The other transport add DEFINE_VIRTIO_COMMON FEATURES in their base
> class. Because of the not-quite-understood problem with virtio-blk, we
> couldn't do that with s390-virtio.

-- 
MST