Re: [PATCH net-next] net: airoha: Add TCP LRO support

[Lorenzo Bianconi <lorenzo@kernel.org>]

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On Jun 10, Eric Dumazet wrote:
> On Tue, Jun 10, 2025 at 2:12 AM Lorenzo Bianconi <lorenzo@kernel.org> wrote:
> >
[...]
> > @@ -767,7 +887,7 @@ static int airoha_qdma_init_rx_queue(struct airoha_queue *q,
> >         int qid = q - &qdma->q_rx[0], thr;
> >         dma_addr_t dma_addr;
> >
> > -       q->buf_size = PAGE_SIZE / 2;
> > +       q->buf_size = pp_params.max_len / (2 * (1 + lro_queue));
> 
> Tell us more... It seems small LRO packets will consume a lot of
> space, incurring a small skb->len/skb->truesize ratio, and bad TCP WAN
> performance.

I think the main idea is forward to hw LRO queues (queues 24-31 in this
case) just specific protocols with mostly big packets but I completely
agree we have an issue for small packets. One possible approach would be
to define a threshold (e.g. 256B) and allocate a buffer or page from the
page allocator for small packets (something similar to what mt7601u driver
is doing[0]).  What do you think?

> 
> And order-5 pages are unlikely to be available in the long run anyway.

I agree. I guess we can reduce the order to ~ 2 (something similar to
mtk_eth_soc hw LRO implementation [1]).

> 
> LRO support would only make sense if the NIC is able to use multiple
> order-0 pages to store the payload.

The hw supports splitting big packets over multiple order-0 pages if we
increase the MTU over one page size, but according to my understanding
hw LRO requires contiguous memory to work.

Regards,
Lorenzo

[0] https://github.com/torvalds/linux/blob/master/drivers/net/wireless/mediatek/mt7601u/dma.c#L146
[1] https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/mediatek/mtk_eth_soc.c#L2258

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