netdev - Re: Fwd: Packet mmap: TX RING and zero copy

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Date:	Mon, 8 Sep 2008 15:01:04 +0200
From:	"Johann Baudy" <johaahn@...il.com>
To:	"Evgeniy Polyakov" <johnpol@....mipt.ru>
Cc:	netdev@...r.kernel.org
Subject: Re: Fwd: Packet mmap: TX RING and zero copy

Hi Evgeniy,

> Are you sure that it is udp_push_pending_frames() and not some splice
> waiting?
>
No, I'm not sure.
Are there any queue or allocator limits that can slow the bitrate
through this function?
I mean something that will need end of transfer to start a new one.

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -743,7 +743,29 @@ int udp_sendpage(struct sock *sk, struct page
*page, int offset,
                 size_t size, int flags)
 {
        struct udp_sock *up = udp_sk(sk);
+       struct inet_sock *inet = inet_sk(sk);
        int ret;
+       int mtu, fragheaderlen;
+       struct ip_options *opt = NULL;
+
+       lock_sock(sk);
+       mtu = inet->cork.fragsize;
+
+       if (inet->cork.flags & IPCORK_OPT)
+               opt = inet->cork.opt;
+
+       fragheaderlen = sizeof(struct iphdr) + (opt ? opt->optlen : 0);
+
+       // With UDP fragmentation
+       if (inet->cork.length + size >= 0xFFFF - fragheaderlen) {
+       // Without UDP fragmentation
+       //  if( (inet->cork.length + size) > mtu) {
+               ret = udp_push_pending_frames(sk);
+               if (ret) {
+                       return 0;
+               }
+       }
+       release_sock(sk);

        if (!up->pending) {
                struct msghdr msg = {   .msg_flags = flags|MSG_MORE };

Please find above, patch with your rectifications.
Do we must use MTU limit instead offset limit? As you said that UDP
split over IP must be avoided.
If yes, can I force size value forwarded to ip_append_page() in order
to fill the whole packet? Or this will not be handled properly by all
callers?

Thanks in advance,
Johann


-- 
Johann Baudy
johaahn@...il.com
--
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