From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751065Ab3GJEYP (ORCPT ); Wed, 10 Jul 2013 00:24:15 -0400 Received: from mail-gh0-f179.google.com ([209.85.160.179]:57117 "EHLO mail-gh0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750736Ab3GJEYO (ORCPT ); Wed, 10 Jul 2013 00:24:14 -0400 Message-ID: <51DCE1EA.60404@gmail.com> Date: Tue, 09 Jul 2013 22:24:10 -0600 From: Robert Hancock User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Pavel Machek CC: Greg KH , kernel list , joe.lawrence@stratus.com, myron.stowe@redhat.com, bhelgaas@google.com Subject: Re: /sys/module/pcie_aspm/parameters/policy not writable? References: <20130709012611.GA22371@amd.pavel.ucw.cz> <20130709041321.GA30555@kroah.com> <20130709094906.GA3870@amd.pavel.ucw.cz> In-Reply-To: <20130709094906.GA3870@amd.pavel.ucw.cz> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/09/2013 03:49 AM, Pavel Machek wrote: > On Mon 2013-07-08 21:13:21, Greg KH wrote: >> On Tue, Jul 09, 2013 at 03:26:11AM +0200, Pavel Machek wrote: >>> Hi! >>> >>> My thinkpad has rather high ping latencies... and perhaps it is due to >>> PCIE ASPM. >> >> Why would that be the problem? The odds that the PCIE bus is the issue >> seems strange to me. > > Aha: I guess that's why the file is not writable: > > pavel@amd:~$ dmesg | grep -i aspm > ACPI FADT declares the system doesn't support PCIe ASPM, so disable it IIRC, this message is somewhat misleading. When that FADT flag is set by the BIOS, the kernel doesn't so much disable ASPM as disable the kernel's control over ASPM. I believe this was to match Windows behavior. > e1000e 0000:02:00.0: Disabling ASPM L0s L1 And given that, I think this message may also be misleading, as the kernel won't touch the device's ASPM state. Force-enabling ASPM may actually be allowing the driver to disable ASPM on the device. I seem to recall a recent thread on this about another device.. maybe we need to allow drivers to explicitly disable ASPM if it's enabled even if the FADT flag is set? > pavel@amd:~$ cat /sys/module/pcie_aspm/parameters/policy > [default] performance powersave > pavel@amd:~$ > root@amd:~# echo -n performance > > /sys/module/pcie_aspm/parameters/policy > -su: echo: write error: Operation not permitted > root@amd:~# > > But: > 1) it should not list unavailable options > > 2) operation not permitted seems like wrong error code for > operation not supported. > > Pavel >