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

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Date:	Mon, 8 Sep 2008 12:21:16 +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,

I've made a test with below patch (with and without UDP fragmentation):

without UDP fragmentation, packet size are almost always equal to
PAGE_SIZE due to my mtu limit (2*PACKET_SIZE > mtu).
with UDP fragmentation, kernel is sending multiple fragmented packets
of 61448Kbytes.

Unfortunately, in both case, bitrate is still 15-20 MB/s :(
According to wireshark, kernel sends 60KB over 9 packets, nothing
during ~5ms, 60KB and so on. strange ... kernel seems to spend its
time during push(). Is there a blocking call somewhere ?

Thanks in advance,
Johann

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c

@@ -743,7 +743,28 @@ 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 = inet->cork.fragsize;
+       int fragheaderlen;
+       struct ip_options *opt = NULL;
+
+       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) {
+               lock_sock(sk);
+               ret = udp_push_pending_frames(sk);
+               release_sock(sk);
+               if (ret) {
+                       return 0;
+               }
+       }





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