Messages in this thread | | | Subject | Re: [PATCH net-next 2/2] virtio-net: fix the XDP truesize calculation for mergeable buffers | From | Jason Wang <> | Date | Fri, 8 May 2020 09:54:05 +0800 |
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On 2020/5/6 下午8:08, Michael S. Tsirkin wrote: > On Wed, May 06, 2020 at 04:21:15PM +0800, Jason Wang wrote: >> On 2020/5/6 下午3:37, Michael S. Tsirkin wrote: >>> On Wed, May 06, 2020 at 02:16:33PM +0800, Jason Wang wrote: >>>> We should not exclude headroom and tailroom when XDP is set. So this >>>> patch fixes this by initializing the truesize from PAGE_SIZE when XDP >>>> is set. >>>> >>>> Cc: Jesper Dangaard Brouer<brouer@redhat.com> >>>> Signed-off-by: Jason Wang<jasowang@redhat.com> >>> Seems too aggressive, we do not use up the whole page for the size. >>> >>> >>> >> For XDP yes, we do: >> >> static unsigned int get_mergeable_buf_len(struct receive_queue *rq, >> struct ewma_pkt_len *avg_pkt_len, >> unsigned int room) >> { >> const size_t hdr_len = sizeof(struct virtio_net_hdr_mrg_rxbuf); >> unsigned int len; >> >> if (room) >> return PAGE_SIZE - room; >> >> ... >> >> Thanks > Hmm. But that's only for new buffers. Buffers that were outstanding > before xdp was attached don't use the whole page, do they?
They don't and in either case, we've encoded truesize in the ctx. Any issue you saw?
> > > > > Also, with TCP smallqueues blocking the queue like that might be a problem. > Could you try and check performance impact of this?
I'm not sure I get you, TCP small queue is more about TX I guess. And since we've invalidated the vnet header, the performance of XDP_PASS won't be good.
> I looked at what other drivers do and I see they tend to copy the skb > in XDP_PASS case. ATM we don't normally - but should we?
My understanding is XDP runs before skb, so I don't get here. Or maybe you can point me the driver you mentioned here? I've checked i40e and mlx5e, both of them build skb after XDP.
Thanks
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