From: Timo Juhani Lindfors <timo.lindfors@iki•fi>
To: David Miller <davem@davemloft•net>
Cc: netdev@vger•kernel.org
Subject: Re: [PATCH] ip: reuse ip_summed of first fragment for all subsequent fragments
Date: Tue, 11 Jan 2011 15:49:19 +0200 [thread overview]
Message-ID: <84mxn7czz4.fsf@sauna.l.org> (raw)
In-Reply-To: <20101228.134905.183040321.davem@davemloft.net> (David Miller's message of "Tue\, 28 Dec 2010 13\:49\:05 -0800 \(PST\)")
David Miller <davem@davemloft•net> writes:
> > - skb->ip_summed = CHECKSUM_NONE;
> > + skb->ip_summed = skb_prev->ip_summed;
> You can't just assign skb_prev->ip_summed here, if it's CHECKSUM_PARTIAL
> then things will go completely wrong. This is especially true since
> we're about to zero out skb->csum.
Thanks, I clearly didn't understand the semantics of ip_summed. For
received packets CHECKSUM_PARTIAL apparently means that the checksum
is calculated by hardware and CHECKSUM_NONE that it is calculated by
software or it is not calculated at all. I guess the ip_summed of a
new fragment is set to CHECKSUM_NONE because hardware can not handle
checksums of fragments?
Anyways, socket option SO_NO_CHECK sets sk->sk_no_check. Could this be
checked before calculating checksums of each fragment? Currently
udp_push_pending_frames checks this but checksums have already been
calculated at that point (and the only job left is to sum the
checksums together). Here's a patch that works for me (=according to
perf time is no longer spent calculating checksums) but probably
should be reviewed carefully:
>From 67fe193db5a2e1a2efaa0fa8e1c1c2554e108b78 Mon Sep 17 00:00:00 2001
From: Timo Juhani Lindfors <timo.lindfors@iki•fi>
Date: Tue, 11 Jan 2011 14:36:23 +0200
Subject: [PATCH] ip: make sure disabling checksums really works
---
net/ipv4/ip_output.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 439d2a3..9bc163a 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -80,6 +80,7 @@
#include <linux/mroute.h>
#include <linux/netlink.h>
#include <linux/tcp.h>
+#include <net/udp.h>
int sysctl_ip_default_ttl __read_mostly = IPDEFTTL;
@@ -1208,7 +1209,7 @@ ssize_t ip_append_page(struct sock *sk, struct page *page,
goto error;
}
- if (skb->ip_summed == CHECKSUM_NONE) {
+ if (skb->ip_summed == CHECKSUM_NONE && sk->sk_no_check != UDP_CSUM_NOXMIT) {
__wsum csum;
csum = csum_page(page, offset, len);
skb->csum = csum_block_add(skb->csum, csum, skb->len);
--
1.7.2.3
next prev parent reply other threads:[~2011-01-11 14:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-14 7:51 [PATCH] ip: use checksum options of first fragment also for subsequent fragments Timo Juhani Lindfors
2010-12-17 19:58 ` David Miller
2010-12-20 10:38 ` [PATCH] ip: reuse ip_summed of first fragment for all " Timo Juhani Lindfors
2010-12-28 21:49 ` David Miller
2011-01-11 13:49 ` Timo Juhani Lindfors [this message]
2011-01-13 2:42 ` David Miller
2011-02-16 9:10 ` Timo Juhani Lindfors
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