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From: Stephen Hemminger <shemminger@vyatta.com>
To: Hagen Paul Pfeifer <hagen@jauu.net>
Cc: netdev@vger.kernel.org, davem@davemloft.net
Subject: Re: [PATCH] net: optimize Berkeley Packet Filter (BPF) processing
Date: Sat, 19 Jun 2010 22:16:11 -0700	[thread overview]
Message-ID: <20100619221611.784f7dbc@nehalam> (raw)
In-Reply-To: <1277003136-5522-1-git-send-email-hagen@jauu.net>

On Sun, 20 Jun 2010 05:05:36 +0200
Hagen Paul Pfeifer <hagen@jauu.net> wrote:

> Gcc is currenlty not in the ability to optimize the switch statement in
> sk_run_filter() because of dense case labels. This patch replace the
> OR'd labels with ordered sequenced case labels. The sk_chk_filter()
> function is modified to patch/replace the original OPCODES in a
> ordered but equivalent form. gcc is now in the ability to transform the
> switch statement in sk_run_filter into a jump table of complexity O(1).
> 
> Until this patch gcc generates a sequence of conditional branches (O(n) of 567
> byte .text segment size (arch x86_64):

I don't think this works because it breaks ABI compatibility for applications tha
use older versions.

  reply	other threads:[~2010-06-20  5:16 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-06-20  3:05 [PATCH] net: optimize Berkeley Packet Filter (BPF) processing Hagen Paul Pfeifer
2010-06-20  5:16 ` Stephen Hemminger [this message]
2010-06-20  9:50   ` Hagen Paul Pfeifer
2010-06-20 18:49     ` Stephen Hemminger
2010-06-20 22:09     ` David Miller
2010-06-20 21:57       ` Hagen Paul Pfeifer
2010-06-21  2:15         ` Changli Gao
2010-06-21  7:57           ` Hagen Paul Pfeifer
2010-06-26  4:36 ` David Miller

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