Patchwork [Fwd:,Re:,[PATCH] x86: Relegate CONFIG_PAT to EMBEDDED]

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Submitter Tim Gardner
Date Oct. 11, 2009, 6:28 p.m.
Message ID <4AD223C3.3020607@canonical.com>
Download mbox | patch
Permalink /patch/35717/
State Accepted
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Comments

Tim Gardner - Oct. 11, 2009, 6:28 p.m.
Andy, Stefan - Why _is_ it that we don't have PAT enabled? Wasn't it
originally a prerequisite for KMS back in Jaunty days?

There are some comments on LKML pointing out that we _should_ have PAT
enabled, e.g., "[RFC Patch] use MTRR for write combining if PAT is not
available"

rtg
Tim Gardner - Oct. 13, 2009, 1:18 a.m.
Tim Gardner wrote:
> Andy, Stefan - Why _is_ it that we don't have PAT enabled? Wasn't it
> originally a prerequisite for KMS back in Jaunty days?
> 
> There are some comments on LKML pointing out that we _should_ have PAT
> enabled, e.g., "[RFC Patch] use MTRR for write combining if PAT is not
> available"
> 
> rtg
> 

http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-karmic.git;a=commit;h=a611fa50121f1698bd367b991f66e2268eb10824
Daniel J Blueman - Oct. 13, 2009, 9:49 a.m.
On Tue, Oct 13, 2009 at 2:18 AM, Tim Gardner <tim.gardner@canonical.com> wrote:
> Tim Gardner wrote:
>> Andy, Stefan - Why _is_ it that we don't have PAT enabled? Wasn't it
>> originally a prerequisite for KMS back in Jaunty days?
>>
>> There are some comments on LKML pointing out that we _should_ have PAT
>> enabled, e.g., "[RFC Patch] use MTRR for write combining if PAT is not
>> available"
>>
>> rtg
>>
>
> http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-karmic.git;a=commit;h=a611fa50121f1698bd367b991f66e2268eb10824

Excellent. Is the idea that this will be a karmic beta update in a
couple of days, and we have a get-out-of-jail of disabling it (or
default boot with 'nopat') before the final release is cut?

Or, is this simply too late to make the final release?

Daniel
Tim Gardner - Oct. 13, 2009, 1:10 p.m.
Daniel J Blueman wrote:
> On Tue, Oct 13, 2009 at 2:18 AM, Tim Gardner <tim.gardner@canonical.com> wrote:
>> Tim Gardner wrote:
>>> Andy, Stefan - Why _is_ it that we don't have PAT enabled? Wasn't it
>>> originally a prerequisite for KMS back in Jaunty days?
>>>
>>> There are some comments on LKML pointing out that we _should_ have PAT
>>> enabled, e.g., "[RFC Patch] use MTRR for write combining if PAT is not
>>> available"
>>>
>>> rtg
>>>
>> http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-karmic.git;a=commit;h=a611fa50121f1698bd367b991f66e2268eb10824
> 
> Excellent. Is the idea that this will be a karmic beta update in a
> couple of days, and we have a get-out-of-jail of disabling it (or
> default boot with 'nopat') before the final release is cut?
> 
> Or, is this simply too late to make the final release?
> 
> Daniel

Kernel freeze is Thursday. With the addition of stable and other
miscellaneous patches, today's upload is going to be the last one
(unless some OMG kitten killer gets in my face).

rtg
Daniel J Blueman - Oct. 13, 2009, 2:15 p.m.
On Tue, Oct 13, 2009 at 2:10 PM, Tim Gardner <tim.gardner@canonical.com> wrote:
> Daniel J Blueman wrote:
>> On Tue, Oct 13, 2009 at 2:18 AM, Tim Gardner <tim.gardner@canonical.com> wrote:
>>> Tim Gardner wrote:
>>>> Andy, Stefan - Why _is_ it that we don't have PAT enabled? Wasn't it
>>>> originally a prerequisite for KMS back in Jaunty days?
>>>>
>>>> There are some comments on LKML pointing out that we _should_ have PAT
>>>> enabled, e.g., "[RFC Patch] use MTRR for write combining if PAT is not
>>>> available"
>>>>
>>>> rtg
>>>>
>>> http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-karmic.git;a=commit;h=a611fa50121f1698bd367b991f66e2268eb10824
>>
>> Excellent. Is the idea that this will be a karmic beta update in a
>> couple of days, and we have a get-out-of-jail of disabling it (or
>> default boot with 'nopat') before the final release is cut?
>>
>> Or, is this simply too late to make the final release?
>>
>> Daniel
>
> Kernel freeze is Thursday. With the addition of stable and other
> miscellaneous patches, today's upload is going to be the last one
> (unless some OMG kitten killer gets in my face).

Ok, great.

Still of importance, so worth mentioning here, CONFIG_X86_MCE gives
visibility of otherwise silent memory controller and/or internal
processor state (including processor passing critical temperature
thresholds).

This is particularly crucial for servers with lots of memory
(therefore higher chance of cell failure), but also modern desktops
having larger amounts of memory. From a support perspective, detected
memory errors are logged to the kernel log. From a user perspective
(particularly for ubuntu-server), the user knows more when they have
eg failing/faulty memory. I'd think twice about deploying critical
services on a server where (un)correctable ECC errors *silently*
occur...

Since this feature has been around really a long time, it carries no
risk. Thoughts?
Tim Gardner - Oct. 13, 2009, 2:58 p.m.
Daniel J Blueman wrote:
> On Tue, Oct 13, 2009 at 2:10 PM, Tim Gardner <tim.gardner@canonical.com> wrote:
>> Daniel J Blueman wrote:
>>> On Tue, Oct 13, 2009 at 2:18 AM, Tim Gardner <tim.gardner@canonical.com> wrote:
>>>> Tim Gardner wrote:
>>>>> Andy, Stefan - Why _is_ it that we don't have PAT enabled? Wasn't it
>>>>> originally a prerequisite for KMS back in Jaunty days?
>>>>>
>>>>> There are some comments on LKML pointing out that we _should_ have PAT
>>>>> enabled, e.g., "[RFC Patch] use MTRR for write combining if PAT is not
>>>>> available"
>>>>>
>>>>> rtg
>>>>>
>>>> http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-karmic.git;a=commit;h=a611fa50121f1698bd367b991f66e2268eb10824
>>> Excellent. Is the idea that this will be a karmic beta update in a
>>> couple of days, and we have a get-out-of-jail of disabling it (or
>>> default boot with 'nopat') before the final release is cut?
>>>
>>> Or, is this simply too late to make the final release?
>>>
>>> Daniel
>> Kernel freeze is Thursday. With the addition of stable and other
>> miscellaneous patches, today's upload is going to be the last one
>> (unless some OMG kitten killer gets in my face).
> 
> Ok, great.
> 
> Still of importance, so worth mentioning here, CONFIG_X86_MCE gives
> visibility of otherwise silent memory controller and/or internal
> processor state (including processor passing critical temperature
> thresholds).
> 
> This is particularly crucial for servers with lots of memory
> (therefore higher chance of cell failure), but also modern desktops
> having larger amounts of memory. From a support perspective, detected
> memory errors are logged to the kernel log. From a user perspective
> (particularly for ubuntu-server), the user knows more when they have
> eg failing/faulty memory. I'd think twice about deploying critical
> services on a server where (un)correctable ECC errors *silently*
> occur...
> 
> Since this feature has been around really a long time, it carries no
> risk. Thoughts?

Frankly, I've no idea why it _isn't_ enabled. Since Karmic is really the
test release for Lucid, I'm gonna turn it on.

http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-karmic.git;a=commit;h=ecae83a7adca974982267a4084a30033de9b6b22

I'm not too concerned about MCE working correctly on 64 bit platforms,
but I've a bit more concern about older 32 bit CPUs.

rtg

Patch

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4427956..2fbc3c6 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1327,7 +1327,9 @@  config MATH_EMULATION
 	  kernel, it won't hurt.
 
 config MTRR
-	bool "MTRR (Memory Type Range Register) support"
+	bool
+	default y
+	prompt "MTRR (Memory Type Range Register) support" if EMBEDDED
 	---help---
 	  On Intel P6 family processors (Pentium Pro, Pentium II and later)
 	  the Memory Type Range Registers (MTRRs) may be used to control
@@ -1393,7 +1395,8 @@  config MTRR_SANITIZER_SPARE_REG_NR_DEFAULT
 
 config X86_PAT
 	bool
-	prompt "x86 PAT support"
+	default y
+	prompt "x86 PAT support" if EMBEDDED
 	depends on MTRR
 	---help---
 	  Use PAT attributes to setup page level cache control.