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

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Date: Tue, 26 Mar 2024 14:35:21 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.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 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?

Thanks