Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762329Ab2FHSDB (ORCPT ); Fri, 8 Jun 2012 14:03:01 -0400 Received: from mail-vc0-f174.google.com ([209.85.220.174]:61162 "EHLO mail-vc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751394Ab2FHSC7 convert rfc822-to-8bit (ORCPT ); Fri, 8 Jun 2012 14:02:59 -0400 MIME-Version: 1.0 In-Reply-To: References: <1339142492-13625-1-git-send-email-xudong.hao@intel.com> Date: Fri, 8 Jun 2012 12:02:55 -0600 Message-ID: Subject: Re: [PATCH 0/4] PCI: Enable LTR/OBFF before device is used by driver From: Myron Stowe To: Bjorn Helgaas Cc: Xudong Hao , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, avi@redhat.com, alex.williamson@redhat.com, ddutile@redhat.com, myron.stowe@redhat.com, xiantao.zhang@intel.com Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2167 Lines: 46 On Fri, Jun 8, 2012 at 11:31 AM, Bjorn Helgaas wrote: > On Fri, Jun 8, 2012 at 1:01 AM, Xudong Hao wrote: >> The series of patches enable LTR and OBFF before device is used by driver, and >> introduce a couple of functions to save/restore LTR latency value. >> >> Patch 1/4 introduce new function pci_obff_supported() as pci_ltr_support(). >> >> Patch 2/4 enable LTR(Latency tolerance reporting) before device is used by >> driver. >> >> Patch 3/4 enable OBFF(optimized buffer flush/fill) before device is used by >> driver. >> >> Patch 4/4 introduce a couple of functions pci_save_ltr_value() and >> pci_restore_ltr_value() to save and restore LTR latency value, while device is >> reset. > > We need some justification for these patches. ?Why do we want them? > Do they improve performance? ?Reduce power consumption? ?How have they > been tested? ?How can we be confident that these features work > correctly on hardware in the field? ?Should or could the BIOS enable > them itself, based on OEM testing and desire to support these > features? I too am a little nervous about these changes due to Jesse's earlier response (see http://marc.info/?l=linux-pci&m=133372610102933&w=2) where he indicated: "Given how device specific these extensions are, I'd expect you'd need to know about each specific device anyway, which is why I think the control belongs in the driver." Having these features enabled by default may be too aggressive. Not saying it is not correct - something you may be able to inform us about, especially since you are with Intel - just make me nervous without further information. Myron > -- > 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/ -- 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/