lkml.org 
[lkml]   [2011]   [Sep]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [RFC PATCH 0/3] Add accurate boot timing to a Linux system
From
Hi Bjorn,

On Sun, Sep 25, 2011 at 5:54 AM, Bjorn Helgaas <bhelgaas@google.com> wrote:
> On Fri, Sep 23, 2011 at 5:03 PM, Simon Glass <sjg@chromium.org> wrote:
>> This experimental patch set adds boot timing to a Linux system. The
>> timing starts with the boot loader and extends through the kernel into
>> user space to the completion of the boot process. The timing starts when
>> the system leaves reset, not later when the kernel starts.
>>
>> The concept is:
>> - Boot loader records a timestamp for key events during its operation
>> - These timestamps are passed to Linux, which adds more as it boots
>> - These timestamps are made available to user space, where more
>> timestamps are added as init does its job
>> - Finally the whole record is collected by a user-space script run at
>> the end of init. This is fed back through some mechanism to monitor
>> boot time in the field.
>
> I think this is a cool idea.  It's quite difficult to extract this
> sort of information today, and making it easily and consistently
> available should help focus attention and improve things.
>
> There are difficult issues about which clock to use, how to correlate
> bootloader & kernel timestamps, how to make sure the timestamps stay
> sensible even when we use hwclock, ntp, etc., but I think it's worth
> pushing on this to see how far you can go.

Yes it is not easy to get all of this right, especially trying to
cross two completely different projects. I think the timestamps should
be measured from reset. The kernel timestamps start not at zero, but
from the time the kernel starts. This guarantees a consistent time
base across the data. Also if there is a pre-boot program (such as a
NAND loader) then its time will be counted also.

A good timer would be an accurate monotonic wall clock, not
necessarily related to time of day. An ideal timer would be a
microsecond/nanosecond timer maintained by the hardware / SOC.

Regards,
Simon

>
> Bjorn
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2011-09-27 20:29    [from the cache]
©2003-2011 Jasper Spaans