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

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Message-ID: <1711523698.8996527-2-xuanzhuo@linux.alibaba.com>
Date: Wed, 27 Mar 2024 15:14:58 +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 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.

>
> Thanks
>