Re: [PATCH 2/2] printk: Add boottime and real timestamps

Prarit Bhargava
2017-07-28T15:01:54Z

On 07/25/2017 09:00 AM, Peter Zijlstra wrote:
> On Tue, Jul 25, 2017 at 08:17:27AM -0400, Prarit Bhargava wrote:
>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>> index 5b1662ec546f..6cd38a25f8ea 100644
>> --- a/lib/Kconfig.debug
>> +++ b/lib/Kconfig.debug
>> @@ -1,8 +1,8 @@
>> menu "printk and dmesg options"
>>
>> config PRINTK_TIME
>> - int "Show timing information on printks (0-1)"
>> - range 0 1
>> + int "Show timing information on printks (0-3)"
>> + range 0 3
>> default "0"
>> depends on PRINTK
>> help
>> @@ -13,7 +13,8 @@ config PRINTK_TIME
>> The timestamp is always recorded internally, and exported
>> to /dev/kmsg. This flag just specifies if the timestamp should
>> be included, not that the timestamp is recorded. 0 disables the
>> - timestamp and 1 uses the local clock.
>> + timestamp and 1 uses the local clock, 2 uses the monotonic clock, and
>> + 3 uses real clock.
>>
>> The behavior is also controlled by the kernel command line
>> parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst
>
>
> choice
> prompt "printk default clock"
> default PRIMTK_TIME_DISABLE
> help
> goes here
>
> config PRINTK_TIME_DISABLE
> bool "Disabled"
> help
> goes here
>
> config PRINTK_TIME_LOCAL
> bool "local clock"
> help
> goes here
>
> config PRINTK_TIME_MONO
> bool "CLOCK_MONOTONIC"
> help
> goes here
>
> config PRINTK_TIME_REAL
> bool "CLOCK_REALTIME"
> help
> goes here
>
> endchoice
>
> config PRINTK_TIME
> int
> default 0 if PRINTK_TIME_DISABLE
> default 1 if PRINTK_TIME_LOCAL
> default 2 if PRINTK_TIME_MONO
> default 3 if PRINTK_TIME_REAL
>
>

Thanks for the above change. I can see that makes the code simpler.

> Although I must strongly discourage using REALTIME, DST will make
> untangling your logs an absolute nightmare. I would simply not provide
> it.

I understand your concern, however, I've been in situations where REALTIME
stamping has pointed me in the direction of where a bug was. Even with the
complicated logs I think it is worthwhile.

P.