From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH 2/5] bitops: compile time optimization for hweight_long(CONSTANT) Date: Wed, 03 Feb 2010 11:49:54 -0800 Message-ID: <4B69D362.10608@zytor.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Borislav Petkov , Andrew Morton , Wu Fengguang , LKML , Jamie Lokier , Roland Dreier , Al Viro , "linux-fsdevel@vger.kernel.org" , Ingo Molnar To: Peter Zijlstra Return-path: 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 In-Reply-To: <1265222875.24455.1020.camel@laptop> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 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