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SubjectRe: [git head] Should X86_PAT really default to yes?
On Sun, May 4, 2008 at 12:10 AM, Frans Pop <> wrote:
> On Friday 02 May 2008, Jesse Barnes wrote:
> > This is just a transient issue during VT switch or server exit though,
> > right? X functionality isn't affected, and your VTs work fine?
> Transient only. I've just tested again and this time the band
> was visible on top of the text on VT1 for about 2 seconds. Then it
> disappeared.
> The artifacts also appear when I log out from KDE (i.e. without exiting the
> server), and I also get the messages when logging out and logging in again.
> I do not see any performance issues, but I've only used this kernel for a
> very short time.
> > If so, it might not be a PAT issue but just a different memory layout or
> > something (and therefore it would really just be a cosmetic bug in the X
> > driver).
> The artifacts may not be a PAT issue directly, but it is a clear regression
> for me as I currently have a nice clean screen when X shuts down. I'm also
> 100% sure that it is caused by enabling PAT. A kernel with same config and
> only PAT disabled does not show the artifacts.
> Would you like me to file a bug against X for these artifacts?
> If so, against what component? The i810 driver or the server?
> On Saturday 03 May 2008, Jesse Barnes wrote:
> > > I don't see these error messages on my 965 here. May be I have different
> > > x version.
> > Hm, yeah that could be. strace would tell us.
> Would you like me to do an strace?
> Attached my Xorg log for basic info (versions are current Debian unstable)
> and the config I used.
> Also attached a dmesg that shows the messages. As you can see there are some
> repeats.
> - first 22 "expected mapping type" when X is started
> - second 22 "expected mapping type" when logging in
> - 9 "freeing invalid memtype" when logging out
> - 22 "expected mapping type" when logging in again
> - 9 "freeing invalid memtype" when logging out again
> - last series "expected mapping type" when restarting X server
> On Saturday 03 May 2008, Jesse Barnes wrote:
> > More recent versions of X will use sysfs rather than /dev/mem (though
> > we're still using the mprotect hack there to give us UC-), so yeah this
> > warning should already be gone in more recent builds.
> On Friday 02 May 2008, Pallipadi, Venkatesh wrote:
> > ... and should not cause any side-effects other than little annoyance.
> On Friday 02 May 2008, Jesse Barnes wrote:
> > I really think PAT should be on by default; if you're running into real
> > functional or performance problems we'd better get them fixed rather than
> > disabling PAT...
> I must say that I'm fairly disappointed by your (plural) attitude to these
> regressions, especially given that you both seem to feel it is important
> that people will actually use PAT.
> I would say that 40+ messages each time I start X is more than "a little
> annoyance", especially if you run logcheck (as I do).
> I also think you both seriously underestimate how it will impact enabling
> PAT, especially by distributions. Although the errors and the artifacts may
> be minor from a technical point of view, they are the sort of issues that
> users file bug reports about. Loads of them!
> So I expect distros will be extremely reluctant to enable PAT when they know
> they can expect this. The fact that the messages will go away at some point
> in the future is absolutely not relevant.
> Add to that the current warning in the Kconfig help:
> Say N here if you see bootup problems (boot crash, boot hang,
> spontaneous reboots) or a non-working video driver.
> Do you really think that distros can afford the risk of such issues in their
> generic kernel images even if it would only affect a small minority of
> their user base? If this warning is realistic then IMHO X86_PAT should
> default to N and be marked "experimental".
> You can be sure that I at least will not be enabling X86_PAT in the near
> future because of these two issues. And given the nature of this option I'm
> quite likely to completely forget about it afterwards...
> That said, I'll be happy to help trace and get these issues fixed.

can you boot with pat=off and send out /proc/mtrr?


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