netdev - Re: [PATCH vhost v5 00/10] virtio: drivers maintain dma info for premapped vq

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Date: Wed, 27 Mar 2024 16:04:02 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: virtualization@...ts.linux.dev,
 "Michael S. Tsirkin" <mst@...hat.com>,
 "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org
Subject: Re: [PATCH vhost v5 00/10] virtio: drivers maintain dma info for premapped vq

On Wed, 27 Mar 2024 15:50:17 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Wed, Mar 27, 2024 at 3:16 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> >
> > On Tue, 26 Mar 2024 14:35:21 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > > On Mon, Mar 25, 2024 at 4:54 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > > >
> > > > As discussed:
> > > >
> > > > http://lore.kernel.org/all/CACGkMEvq0No8QGC46U4mGsMtuD44fD_cfLcPaVmJ3rHYqRZxYg@mail.gmail.com
> > > >
> > > > If the virtio is premapped mode, the driver should manage the dma info by self.
> > > > So the virtio core should not store the dma info. We can release the memory used
> > > > to store the dma info.
> > > >
> > > > For virtio-net xmit queue, if the virtio-net maintains the dma info,
> > > > the virtio-net must allocate too much memory(19 * queue_size for per-queue), so
> > > > we do not plan to make the virtio-net to maintain the dma info by default. The
> > > > virtio-net xmit queue only maintain the dma info when premapped mode is enable
> > > > (such as AF_XDP is enable).
> > > >
> > > > So this patch set try to do:
> > > >
> > > > 1. make the virtio core to do not store the dma info when driver can do that
> > > >     - But if the desc_extra has not dma info, we face a new question,
> > > >       it is hard to get the dma info of the desc with indirect flag.
> > > >       For split mode, that is easy from desc, but for the packed mode,
> > > >       it is hard to get the dma info from the desc. And hardening
> > > >       the dma unmap is safe, we should store the dma info of indirect
> > > >       descs when the virtio core does not store the bufer dma info.
> > > >
> > > >       The follow patches to this:
> > > >          * virtio_ring: packed: structure the indirect desc table
> > > >          * virtio_ring: split: structure the indirect desc table
> > > >
> > > >     - On the other side, in the umap handle, we mix the indirect descs with
> > > >       other descs. That make things too complex. I found if we we distinguish
> > > >       the descs with VRING_DESC_F_INDIRECT before unmap, thing will be clearer.
> > > >
> > > >       The follow patches do this.
> > > >          * virtio_ring: packed: remove double check of the unmap ops
> > > >          * virtio_ring: split: structure the indirect desc table
> > > >
> > > > 2. make the virtio core to enable premapped mode by find_vqs() params
> > > >     - Because the find_vqs() will try to allocate memory for the dma info.
> > > >       If we set the premapped mode after find_vqs() and release the
> > > >       dma info, that is odd.
> > > >
> > > >
> > > > Please review.
> > > >
> > > > Thanks
> > >
> > > This doesn't apply cleany on vhost.git linux-next branch.
> > >
> > > Which tree is this based on?
> >
> >
> > Sorry. That is on the top of "[PATCH vhost v5 0/6] refactor the params of
> > find_vqs()".
> >
> > Lore-URL: http://lore.kernel.org/all/20240325090419.33677-1-xuanzhuo@linux.alibaba.com
> >
> > Thanks.
>
> I've tried that but it doesn't work:
>
> % git am ~/Downloads/\[PATCH\ vhost\ v5\ 01_10\]\ virtio_ring_\
> introduce\ vring_need_unmap_buffer.eml
> Applying: virtio_ring: introduce vring_need_unmap_buffer
> error: patch failed: drivers/virtio/virtio_ring.c:2080
> error: drivers/virtio/virtio_ring.c: patch does not apply
> Patch failed at 0001 virtio_ring: introduce vring_need_unmap_buffer
> hint: Use 'git am --show-current-patch=diff' to see the failed patch
> When you have resolved this problem, run "git am --continue".
> If you prefer to skip this patch, run "git am --skip" instead.
> To restore the original branch and stop patching, run "git am --abort".
>
> I'm using vhost.git linux-next branch, HEAD is
>
> commit 56e71885b0349241c07631a7b979b61e81afab6a
> Author: Maxime Coquelin <maxime.coquelin@...hat.com>
> Date:   Tue Jan 9 12:10:24 2024 +0100
>
>     vduse: Temporarily fail if control queue feature requested


NOT ON the vhost directly.

That is on the top of "refactor the params of find_vqs"

"refactor the params of find_vqs" said:

	"""
	This pathset is splited from the

	     http://lore.kernel.org/all/20240229072044.77388-1-xuanzhuo@linux.alibaba.com

	That may needs some cycles to discuss. But that notifies too many people.
	"""

But now that is broken due to the change of the that patch set.

I will post the new version of these two patch set soon.

Thanks.


>
> Thanks
>
> >
> > >
> > > Thanks
> > >
> >
>