From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754504AbcCHAm7 (ORCPT ); Mon, 7 Mar 2016 19:42:59 -0500 Received: from g4t3427.houston.hp.com ([15.201.208.55]:56487 "EHLO g4t3427.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754441AbcCHAmg (ORCPT ); Mon, 7 Mar 2016 19:42:36 -0500 Message-ID: <1457400913.15454.435.camel@hpe.com> Subject: Re: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled" From: Toshi Kani To: Paul Gortmaker Cc: Borislav Petkov , Richard Purdie , Toshi Kani , Bruce Ashfield , "Hart, Darren" , "saul.wold" , linux-kernel@vger.kernel.org Date: Mon, 07 Mar 2016 18:35:13 -0700 In-Reply-To: <1457398578.15454.421.camel@hpe.com> References: <20160303205924.GA25222@windriver.com> <1457067768.15454.181.camel@hpe.com> <20160304183713.GA26051@windriver.com> <1457129560.15454.266.camel@hpe.com> <20160307003501.GB26051@windriver.com> <1457366596.15454.281.camel@hpe.com> <20160307210852.GC26051@windriver.com> <1457393912.15454.419.camel@hpe.com> <20160307235328.GD26051@windriver.com> <1457398578.15454.421.camel@hpe.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.18.4 (3.18.4-1.fc23) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2016-03-07 at 17:56 -0700, Toshi Kani wrote: > On Mon, 2016-03-07 at 18:53 -0500, Paul Gortmaker wrote: > > [Re: runtime regression with "x86/mm/pat: Emulate PAT when it is > > disabled"] On 07/03/2016 (Mon 16:38) Toshi Kani wrote: > > > > > On Mon, 2016-03-07 at 16:08 -0500, Paul Gortmaker wrote: > > > > [dropping oe list and lkml since attaching dmesg files.] > > > > > > > > [...] > > > > > > > Yes, please send me full dmesg files.  Since I do not know your > > > > > original state, the diff does not give me the whole picture. > > > > > > > > Attached. > > > > > > Thanks for the dmesg files!  As I suspected, there is no message from > > > pat_init() in both cases.  That is, you are missing the following > > > message, > > > which shows how PAT is configured to support cache attributes. > > > > > > # dmesg | grep PAT > > > [0.000000] x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB  WC  UC- > > > WT   > > > > Interesting... > > > > > > > > It may have seemed working before, but you did not have WC configured > > > to PAT without calling pat_init().  There was not a proper check in > > > place to detect this error before.  Can you please check your code to > > > see what caused this skip of pat_init()?  If you have a git tree, I > > > can > > > take a look as well.  > > > > You already have git copies of what I'm running, since it is vanilla > > mainline commits.  No code changes at this end whatsoever.  I did the > > bisect on vanilla mainline.  All I took from yocto was their ".config" > > > > To recap, v4.1-rc5-21-g9dac62909451 works,  v4.1-rc5-22-g9cd25aac1f44 > > fails, and v4.5-rc6 also fails.  If pat_init() isn't called then this > > is a bug in current mainline.  I'll have a look later myself and see > > if I can trace out how we expect to get to pat_init() and how that > > might be skipped inadvertently unless someone beats me to it. > > Oh, I see.  Can you send me the ".config" file? And also an output of /proc/cpuinfo, please? I think I know what's going on.  I noticed that you have the following message in your dmesg files.  [    0.000000] MTRR: Disabled MTRR is set to disabled when your CPU is Intel but does not support MTRR.  Perhaps, QEMU does not emulate MTRR? pat_init() is not called when MTRR is disabled.  I think this dependency is wrong, and it needs to be fixed. This issue has been there for a long time, and you have been running essentially as PAT disabled in the past.  The commit in question simply detected this issue. Thanks, -Toshi