Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755115AbYCUJSR (ORCPT ); Fri, 21 Mar 2008 05:18:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752921AbYCUJSB (ORCPT ); Fri, 21 Mar 2008 05:18:01 -0400 Received: from rv-out-0910.google.com ([209.85.198.189]:52921 "EHLO rv-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752832AbYCUJSA (ORCPT ); Fri, 21 Mar 2008 05:18:00 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=AM+bN1zC7e7LJFHnaqh+5wkyTfZA64MP31moZ4GgE1z0lgKv2xaei8f26Bw4NN5N0Bwtqu8kNO31yqkga+BTDtm1pNxM+02/rXokywvpmAe5r80EjjFyKPGmBdeUYOaG+zRKW0V8aBHaFMqNH2T/eTdT1JnkBqLLuovOCfyDG/s= Message-ID: <86802c440803210217p2793195bj989be0b25017414@mail.gmail.com> Date: Fri, 21 Mar 2008 02:17:57 -0700 From: "Yinghai Lu" To: "Ingo Molnar" Subject: Re: [patch 1/4] x86: vSMP: Fix is_vsmp_box() Cc: "Ravikiran G Thirumalai" , "Andrew Morton" , linux-kernel@vger.kernel.org, "Glauber de Oliveira Costa" , "Andi Kleen" , shai@scalex86.org In-Reply-To: <20080321091139.GD20420@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080320073740.GA9414@localdomain> <20080320073902.GB9414@localdomain> <86802c440803200044g54617517k4530db76ebe2cabb@mail.gmail.com> <20080320184045.GA6085@localdomain> <20080321091139.GD20420@elte.hu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2365 Lines: 66 On Fri, Mar 21, 2008 at 2:11 AM, Ingo Molnar wrote: > > * Ravikiran G Thirumalai wrote: > > > > >> /* Check if we are running on a ScaleMP vSMP box */ > > >> - if (read_pci_config(0, 0x1f, 0, PCI_VENDOR_ID) == > > >> - (PCI_VENDOR_ID_SCALEMP || (PCI_DEVICE_ID_SCALEMP_VSMP_CTL << 16))) > > >> + if ((read_pci_config_16(0, 0x1f, 0, PCI_VENDOR_ID) == > > >> + PCI_VENDOR_ID_SCALEMP) && > > >> + (read_pci_config_16(0, 0x1f, 0, PCI_DEVICE_ID) == > > >> + PCI_DEVICE_ID_SCALEMP_VSMP_CTL)) > > >> vsmp = 1; > > >> > > >> return vsmp; > > > > > >why read two times > > > > > > > Well, the pci cfg space read happens just _once_ during the boot, as > > the result is cached in a static flag. The above code is better > > readable. So readability is better than micro-optimization here. > > i think the patch below results in even more readable and a bit smaller > code - because it's such a simple check? > > OTOH, you are right in general, for example in mmconf-fam10h_64.c's > get_fam10h_pci_mmconf_base() function, we do this: > > id = read_pci_config(bus, slot, 0, PCI_VENDOR_ID); > > vendor = id & 0xffff; > device = (id>>16) & 0xffff; > if (pci_probes[i].vendor == vendor && > pci_probes[i].device == device) { > > here it would indeed be cleaner to simply do: > > vendor = read_pci_config_16(bus, slot, 0, PCI_VENDOR_ID); > device = read_pci_config_16(bus, slot, 0, PCI_DEVICE_ID); > > instead of open-coding the 16-bit splitting. > > Ingo > > ------------> > Subject: x86: vsmp fix x86 vsmp fix is vsmp box cleanup > From: Ingo Molnar > Date: Fri Mar 21 09:55:06 CET 2008 > > code got a bit smaller: > > arch/x86/kernel/vsmp_64.o: > > text data bss dec hex filename > 205 4 0 209 d1 vsmp_64.o.before > 181 4 0 185 b9 vsmp_64.o.after good evidence. YH -- 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/