linux-kernel - Re: time stamped printks

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Date:	Thu, 08 May 2008 14:10:21 +0200
From:	Hinko Kočevar <hinko.kocevar@...rtapot.si>
To:	Gabriel C <nix.or.die@...glemail.com>
Cc:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org
Subject: Re: time stamped printks

Gabriel C wrote:
> David Miller wrote:
>> From: Hinko Kočevar <hinko.kocevar@...rtapot.si>
>> Date: Thu, 08 May 2008 10:26:01 +0200
>>
>>> Hi all,
>>>
>>> I'm building latest GIT tree kernel for CRIS architecture. Right now I'm seeing 
>>> some strange values with printk stamps - at the start they are initialized to 0, 
>>> but quickly change to 42949372 - 0x028F5AFC.
>>>
>>> Any thoughts to where to look for fix?
>> Very early in the boot, the timestamp counter fetching infrastructure
>> isn't setup yet.  So zero is reported for the timestamp.
>>
>> So early on in the boot, it is often not even possible to setup
>> such things yet.  Because infrastructure they need for probing
>> etc. isn't even available yet.
>>
>> This happens on basically every single Linux platform, there
>> isn't really anything to fix.

Hmm, I was under the impression that this was not an issue (at least not in 2.6.25).

> 
> For the early boot 0's it is normal but not for the following strange values :)

I agree.

> 
> I got the same problem on my 64bit box with latest git head and bisected it down to 3e51f33fcc7f55e6df25d15b55ed10c8b4da84cd
> 
> http://lkml.org/lkml/2008/5/8/146

Well, cris architecture does not have CONFIG_HAVE_UNSTABLE_SCHED_CLOCK. I guess 
sched rework broker something since it was touched by the above commit, or..:

# CONFIG_CGROUPS is not set
CONFIG_GROUP_SCHED=y
CONFIG_FAIR_GROUP_SCHED=y
# CONFIG_RT_GROUP_SCHED is not set
CONFIG_USER_SCHED=y
# CONFIG_CGROUP_SCHED is not set



 From the 3e51f33fcc7f55e6df25d15b55ed10c8b4da84cd commit Changelog:
  - architectures that have an 'imperfect' hardware clock can set
    CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

How can one do that? Just add it to the .config?

Regards,
Hinko


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