[U-Boot] [PATCH 0/4] Accurate boot time measurement

[Wolfgang Denk]

Dear Simon Glass,

In message <1305319923-9477-1-git-send-email-sjg at chromium.org> you wrote:
> This defines the basics of a new boot time measurement feature. This allows
> logging of very accurate time measurements as the boot proceeds, by using
> an available microsecond counter.

Well, as long as we talk about microsecond resolution, I do not see
the compelling advantage over the classic method of timing the output
on the serial console port.  At 115200 bps we have a "resolution" of
better than 0.1 millisecond per character; this should be precise
enough for most practical purposes.

Logging and timing the serial output has a number of advantages over
other solutions:

- It requires zero code changes.  You can run the production code and
  time it.  You can use it without rebuilding / reinstalling the
  software, yes even without access to the source code.
- It is completely platform, SoC and board idependent - we do not need
  to provide any specific timer servcies etc. which are inherently
  platform-dependent.
- It does not cause execution overhead on the running system - it
  affects neither the execution speed not the memory footprint of the
  target under test.

Can you please explain where your solution is better than this
approach, i. e. which problems can be addressed with your code where
the output timing method cannot be used, or where it is less
efficient?

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"Oh dear, I think you'll find reality's on the blink again."
- Marvin The Paranoid Android