Re: [PATCH net-next] xsk: introduce xsk_dma_ops

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


On Mon, 17 Apr 2023 18:19:50 -0700, Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
> On Tue, 18 Apr 2023 09:07:30 +0800 Jason Wang wrote:
> > > > Would you mind explaining this a bit more to folks like me who are not
> > > > familiar with VirtIO?  DMA API is supposed to hide the DMA mapping
> > > > details from the stack, why is it not sufficient here.
> >
> > The reason is that legacy virtio device don't use DMA(vring_use_dma_api()).
> >
> > The AF_XDP assumes DMA for netdev doesn't work in this case. We need a
> > way to make it work.
> Can we not push this down to be bus level? virtio has its own bus it
> can plug in whatever magic it wants into dma ops.

It is actually not possible.


> Doesn't have to be super fast for af_xdp's sake - for af_xdp dma mapping
> is on the control path. You can keep using the if (vring_use_dma_api())
> elsewhere for now if there is a perf concern.

Sorry, I don't particularly understand this passage.

Now, the question is if vring_use_dma_api() is false, then we cannot use DMA

The good news is that except for some of sync's operations, they are in the
control path. I think it is very small effect on performance. Because in most
case the sync is unnecessary.

> Otherwise it really seems like we're bubbling up a virtio hack into
> generic code :(

Can we understand the purpose of this matter to back the DMA operation to the
driver? Although I don't know if there are other drivers with similar


Virtualization mailing list

[Index of Archives]     [KVM Development]     [Libvirt Development]     [Libvirt Users]     [CentOS Virtualization]     [Netdev]     [Ethernet Bridging]     [Linux Wireless]     [Kernel Newbies]     [Security]     [Linux for Hams]     [Netfilter]     [Bugtraq]     [Yosemite Forum]     [MIPS Linux]     [ARM Linux]     [Linux RAID]     [Linux Admin]     [Samba]

  Powered by Linux