netdev - Re: [PATCH net-next v2] xsk: add indirect call for xsk_destruct

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Message-ID: <CAL+tcoCu=7MFm9kioQnQmAQYkqbC_PNr-j3UyVEqyxhe7T2Fig@mail.gmail.com>
Date: Thu, 30 Oct 2025 19:17:27 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Paolo Abeni <pabeni@...hat.com>, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, bjorn@...nel.org, magnus.karlsson@...el.com, 
	maciej.fijalkowski@...el.com, jonathan.lemon@...il.com, sdf@...ichev.me, 
	ast@...nel.org, daniel@...earbox.net, hawk@...nel.org, 
	john.fastabend@...il.com, joe@...a.to, willemdebruijn.kernel@...il.com, 
	bpf@...r.kernel.org, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v2] xsk: add indirect call for xsk_destruct_skb

On Thu, Oct 30, 2025 at 7:00 PM Alexander Lobakin
<aleksander.lobakin@...el.com> wrote:
>
> From: Paolo Abeni <pabeni@...hat.com>
> Date: Thu, 30 Oct 2025 11:15:18 +0100
>
> > On 10/26/25 3:58 PM, Jason Xing wrote:
> >> From: Jason Xing <kernelxing@...cent.com>
> >>
> >> Since Eric proposed an idea about adding indirect call for UDP and
> >
> > Minor nit:                          ^^^^^^
> >
> > either 'remove an indirect call' or 'adding indirect call wrappers'
> >
> >> managed to see a huge improvement[1], the same situation can also be
> >> applied in xsk scenario.
> >>
> >> This patch adds an indirect call for xsk and helps current copy mode
> >> improve the performance by around 1% stably which was observed with
> >> IXGBE at 10Gb/sec loaded.
> >
> > If I follow the conversation correctly, Jakub's concern is mostly about
> > this change affecting only the copy mode.
> >
> > Out of sheer ignorance on my side is not clear how frequent that
> > scenario is. AFAICS, applications could always do zero-copy with proper
> > setup, am I correct?!?
>
> It is correct only when the target driver implements zero-copy
> driver-side XSk. While it's true for modern Ethernet drivers for real
> NICs, "virtual" drivers like virtio-net, veth etc. usually don't have it.
> It's not as common usecase as using XSk on real NICs, but still valid
> and widely used.
> For example, virtio-net has a shortcut where it can send XSk skbs
> without copying everything from the userspace (the no-linear-head mode),
> so there generic XSk mode is way faster there than usually.
>
> Also worth noting that there were attempts to introduce driver-side XSk
> zerocopy for virtio-net (and probably veth, I don't remember) on LKML,
> but haven't been upstreamed yet.

Thanks for the added context. One minor thing I need to say is that
virtio_net has zc mode but it requires the host to support a series of
features which means at a hyperscaler it's really hard to ask hosts to
upgrade their kernels and on the contrary it's effortless to upgrade
VMs. Indeed, veth doesn't have zc mode.

Thanks,
Jason