From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hagen Paul Pfeifer Subject: Re: [PATCH] net: optimize Berkeley Packet Filter (BPF) processing Date: Sun, 20 Jun 2010 23:57:44 +0200 Message-ID: <20100620215743.GA4036@nuttenaction> References: <1277003136-5522-1-git-send-email-hagen@jauu.net> <20100619221611.784f7dbc@nehalam> <20100620095019.GA32223@nuttenaction> <20100620.150928.245399526.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: shemminger@vyatta.com, netdev@vger.kernel.org, Linus Torvalds To: David Miller Return-path: Received: from alternativer.internetendpunkt.de ([88.198.24.89]:33354 "EHLO geheimer.internetendpunkt.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754491Ab0FTW5r (ORCPT ); Sun, 20 Jun 2010 18:57:47 -0400 Content-Disposition: inline In-Reply-To: <20100620.150928.245399526.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: * David Miller | 2010-06-20 15:09:28 [-0700]: >I think from this perspective, the change is fine too, nothing visible >to the user is being changed here. Fine! I have a fundamental question: can we start to use a C language extension, known as "Labels as Values" in the kernel? I checked this and at least gcc, llvm and icc support this extension (btw: c1x[1] don't mention this): static int sk_run_filter(struct sock_filter *filter) { static const void *codetable[] = { &&BPF_S_RET_K, &&BPF_S_ALU_ADD_X, &&BPF_S_ALU_SUB_X, &&BPF_S_ALU_MUL_X }; int pc = 0; goto *codetable[*(filter[pc++].code)]; BPF_S_RET_K: return k; BPF_S_ALU_ADD_X: A += X; goto *codetable[*(filter[pc++].code)]; BPF_S_ALU_SUB_X: A -= X; goto *codetable[*(filter[pc++].code)]; BPF_S_ALU_MUL_X: A *= X goto *codetable[*(filter[pc++].code)]; } At least for gcc and llvm the results are quite impressive: http://llvm.org/bugs/show_bug.cgi?id=3120 arch/m68k/amiga/config.c:amiga_reset() seems to be the only user in the kernel who use this extension (and nobody complains? ;-) Cheers, Hagen [1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1425.pdf -- Hagen Paul Pfeifer || http://blog.jauu.net/ Telephone: +49 174 5455209 || Key Id: 0x98350C22 Key Fingerprint: 490F 557B 6C48 6D7E 5706 2EA2 4A22 8D45 9835 0C22