Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757284AbYGHAir (ORCPT ); Mon, 7 Jul 2008 20:38:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754876AbYGHAii (ORCPT ); Mon, 7 Jul 2008 20:38:38 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:37369 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754091AbYGHAih (ORCPT ); Mon, 7 Jul 2008 20:38:37 -0400 Date: Mon, 7 Jul 2008 17:37:57 -0700 (PDT) From: Linus Torvalds To: Roland McGrath cc: Ingo Molnar , Thomas Gleixner , Andrew Morton , Alexander Viro , Eric Paris , linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/4] x86_64 ia32 syscall audit fast-path In-Reply-To: <20080708000233.E8EF3154244@magilla.localdomain> Message-ID: References: <20080707065615.77BD9154246@magilla.localdomain> <20080707065742.7C119154246@magilla.localdomain> <20080708000233.E8EF3154244@magilla.localdomain> User-Agent: Alpine 1.10 (LFD 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 930 Lines: 27 On Mon, 7 Jul 2008, Roland McGrath wrote: > > Is bt slower than testl? On many microarchitectures, yes. Especially for a memory operand. That said, depending on the size of the constant, 'bt' may be _smaller_ than testl (8-bit constant vs 32-bit one). Which can make up for it. > (I used bt there because I saw it used in entry_64.S for all cases > of testing for only one bit at a time. I haven't checked recent CPU's, it may not matter much on ones that support 64-bit. But bt with a memop was traditionally quite a bit more expensive than 'test'. I too am too lazy to check. Once it's in the slow-path, it doesn't much matter. We're talking a few cycles here. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/