lkml.org 
[lkml]   [2016]   [Mar]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"
From
Date
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

\
 
 \ /
  Last update: 2016-03-08 02:21    [W:0.259 / U:0.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site