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

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Message-ID: <e290a675-fc1e-4edf-833c-aa82af073d30@intel.com>
Date: Thu, 30 Oct 2025 11:59:58 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Paolo Abeni <pabeni@...hat.com>
CC: Jason Xing <kerneljasonxing@...il.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

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.

> 
> In such case I think this patch is not worth.
> 
> Otherwise, please describe/explain the real-use case needing the copy mode.
> 
> Thanks,
> 
> Paolo

Thanks,
Olek