From: Kurt Garloff <garloff@suse.de>
To: Linux kernel list <linux-kernel@vger.kernel.org>,
netfilter-devel@lists.netfilter.org
Subject: [PATCH] Unaligend accesses nulldevname
Date: Thu, 8 Jan 2004 00:00:11 +0100 [thread overview]
Message-ID: <20040107230011.GG23133@tpkurt.garloff.de> (raw)
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Hi,
I found an excessive amount of unaligned accesses on my AXP workstation
and tracked it down to ip_packet_match() in the ip_tables module.
indev and outdev are not properly aligned if set to nulldevname in
ipt_do_table().
This destroys the benefits of comparing names in units of (long) and
on architectures with expensive unaligned accesses (such as ia64 or
alpha), it even hurts a lot.
Find attached a patch against 2.6.0. A similar patch is needed for 2.4,
also attached.
Please consider merging them.
Looking at ip_packet_match(), I have two more thoughts:
* It should not be inlined. It's too large to benefit from inlining,
IMHO. (OTOH, it's only called from one place, so it does not
really matter.)
* There's a comment about the compiler being able to unroll the 2/4
(64/32bit) iter loop which is not completely appropriate: We don't
pass -funroll-loops, so gcc does not do it :-(
It would be beneficial though.
Regards,
--
Kurt Garloff <garloff@suse.de> Cologne, DE
SUSE LINUX AG, Nuernberg, DE SUSE Labs (Head)
[-- Attachment #1.2: iptables-nulldevname-unaligned26.diff --]
[-- Type: text/plain, Size: 445 bytes --]
--- linux-2.6.0.ix86/net/ipv4/netfilter/ip_tables.c.orig 2003-12-18 03:58:28.000000000 +0100
+++ linux-2.6.0.ix86/net/ipv4/netfilter/ip_tables.c 2004-01-07 23:49:29.000000000 +0100
@@ -260,7 +260,7 @@
struct ipt_table *table,
void *userdata)
{
- static const char nulldevname[IFNAMSIZ];
+ static const char nulldevname[IFNAMSIZ] __attribute__((aligned(sizeof(long))));
u_int16_t offset;
struct iphdr *ip;
u_int16_t datalen;
[-- Attachment #1.3: iptables-nulldevname-unaligned24.diff --]
[-- Type: text/plain, Size: 449 bytes --]
--- linux-2.4.19/net/ipv4/netfilter/ip_tables.c 2002-02-25 20:38:14.000000000 +0100
+++ linux-2.4.19.AXP/net/ipv4/netfilter/ip_tables.c 2004-01-09 01:55:01.000000000 +0100
@@ -259,7 +264,7 @@
struct ipt_table *table,
void *userdata)
{
- static const char nulldevname[IFNAMSIZ] = { 0 };
+ static const char nulldevname[IFNAMSIZ] __attribute__((aligned(sizeof(long)))) = { 0 };
u_int16_t offset;
struct iphdr *ip;
void *protohdr;
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next reply other threads:[~2004-01-07 23:00 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-01-07 23:00 Kurt Garloff [this message]
2004-01-11 10:01 ` [PATCH] Unaligend accesses nulldevname Harald Welte
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