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From: "Michael S. Tsirkin" <mst@redhat.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: jasowang@redhat.com, john.r.fastabend@intel.com,
	netdev@vger.kernel.org, alexei.starovoitov@gmail.com,
	daniel@iogearbox.net
Subject: Re: [net PATCH v5 6/6] virtio_net: XDP support for adjust_head
Date: Mon, 23 Jan 2017 21:22:36 +0200	[thread overview]
Message-ID: <20170123205957-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20170117222259.20280.24625.stgit@john-Precision-Tower-5810>

On Tue, Jan 17, 2017 at 02:22:59PM -0800, John Fastabend wrote:
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 62dbf4b..3b129b4 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -41,6 +41,9 @@
>  #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
>  #define GOOD_COPY_LEN	128
>  
> +/* Amount of XDP headroom to prepend to packets for use by xdp_adjust_head */
> +#define VIRTIO_XDP_HEADROOM 256
> +
>  /* RX packet size EWMA. The average packet size is used to determine the packet
>   * buffer size when refilling RX rings. As the entire RX ring may be refilled
>   * at once, the weight is chosen so that the EWMA will be insensitive to short-

I wonder where does this number come from?  This is quite a lot and
means that using XDP_PASS will slow down any sockets on top of it.
Which in turn means people will try to remove XDP when not in use,
causing resets.  E.g. build_skb (which I have a patch to switch to) uses
a much more reasonable NET_SKB_PAD.

-- 
MST

  parent reply	other threads:[~2017-01-23 19:22 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-17 22:19 [net PATCH v5 0/6] virtio_net XDP fixes and adjust_header support John Fastabend
2017-01-17 22:19 ` [net PATCH v5 1/6] virtio_net: use dev_kfree_skb for small buffer XDP receive John Fastabend
2017-01-18 15:48   ` Michael S. Tsirkin
2017-01-23 21:08   ` Michael S. Tsirkin
2017-01-23 21:57     ` John Fastabend
2017-01-24 19:43     ` David Miller
2017-01-24 20:08       ` Michael S. Tsirkin
2017-01-24 20:11         ` David Miller
2017-01-24 20:54           ` Michael S. Tsirkin
2017-01-25  2:57         ` Jason Wang
2017-01-25  3:23           ` Michael S. Tsirkin
2017-01-25  4:02             ` John Fastabend
2017-01-25  5:46               ` Jason Wang
2017-01-25 14:47                 ` Michael S. Tsirkin
2017-01-25 14:45               ` Michael S. Tsirkin
2017-01-17 22:20 ` [net PATCH v5 2/6] virtio_net: wrap rtnl_lock in test for calling with lock already held John Fastabend
2017-01-17 22:21 ` [net PATCH v5 3/6] virtio_net: factor out xdp handler for readability John Fastabend
2017-01-18 15:48   ` Michael S. Tsirkin
2017-01-17 22:21 ` [net PATCH v5 4/6] virtio_net: remove duplicate queue pair binding in XDP John Fastabend
2017-01-18 15:49   ` Michael S. Tsirkin
2017-01-17 22:22 ` [net PATCH v5 5/6] virtio_net: refactor freeze/restore logic into virtnet reset logic John Fastabend
2017-01-18 15:50   ` Michael S. Tsirkin
2017-01-17 22:22 ` [net PATCH v5 6/6] virtio_net: XDP support for adjust_head John Fastabend
2017-01-18  3:35   ` Jason Wang
2017-01-18 15:15   ` Michael S. Tsirkin
2017-01-19  3:05     ` Jason Wang
2017-01-19 21:11       ` Michael S. Tsirkin
2017-01-20  3:26         ` Jason Wang
2017-01-20  3:39           ` John Fastabend
2017-01-20  3:38         ` John Fastabend
2017-01-20 16:59         ` David Laight
2017-01-20 17:48           ` Michael S. Tsirkin
2017-01-22  2:51             ` Jason Wang
2017-01-22  4:14               ` John Fastabend
2017-01-23 17:02                 ` Michael S. Tsirkin
2017-01-23 19:22   ` Michael S. Tsirkin [this message]
2017-01-23 20:09     ` Michael S. Tsirkin
2017-01-23 22:12       ` John Fastabend
2017-01-23 22:28         ` Michael S. Tsirkin
2017-01-18 15:48 ` [net PATCH v5 0/6] virtio_net XDP fixes and adjust_header support Michael S. Tsirkin

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