Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757726Ab0BCTz7 (ORCPT ); Wed, 3 Feb 2010 14:55:59 -0500 Received: from terminus.zytor.com ([198.137.202.10]:48732 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757095Ab0BCTzz (ORCPT ); Wed, 3 Feb 2010 14:55:55 -0500 Message-ID: <4B69D362.10608@zytor.com> Date: Wed, 03 Feb 2010 11:49:54 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.7) Gecko/20100120 Fedora/3.0.1-1.fc12 Thunderbird/3.0.1 MIME-Version: 1.0 To: Peter Zijlstra CC: Borislav Petkov , Andrew Morton , Wu Fengguang , LKML , Jamie Lokier , Roland Dreier , Al Viro , "linux-fsdevel@vger.kernel.org" , Ingo Molnar Subject: Re: [PATCH 2/5] bitops: compile time optimization for hweight_long(CONSTANT) References: <20100130094515.475881280@intel.com> <20100130094957.692671259@intel.com> <20100201124825.cc024f2a.akpm@linux-foundation.org> <20100203133951.GA24357@localhost> <20100203070825.e36b3932.akpm@linux-foundation.org> <1265210157.24455.646.camel@laptop> <20100203074251.e2caa3f3.akpm@linux-foundation.org> <20100203181425.GB1367@aftab> <1265222875.24455.1020.camel@laptop> In-Reply-To: <1265222875.24455.1020.camel@laptop> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 824 Lines: 20 On 02/03/2010 10:47 AM, Peter Zijlstra wrote: > On Wed, 2010-02-03 at 19:14 +0100, Borislav Petkov wrote: > >> alternative("call hweightXX", "popcnt", X86_FEATURE_POPCNT) > > Make sure to apply a 0xff bitmask to the popcnt r16 call for hweight8(), > and hweight64() needs a bit of magic for 32bit, but yes, something like > that ought to work nicely. > Arguably the "best" option is to have the alternative being a jump to an out-of-line stub which does the necessary parameter marshalling before calling a stub. This technique is already used in a few other places. -hpa -- 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/