On Fri, Aug 17, 2007 at 08:22:40AM +1000, Paul Mackerras wrote:
OK, so to keep the tools happy, the total time needs to add up
to wall-clock time. Which tells me that the "scaled idle time"
should be defined as "wall clock time minus the other stuff".
Yes, good, that's what I was expecting. As a sysadmin and/or
back-of-the-envelope performance person, I would certainly like
to have ps and top report the scaled time. When I do "performance
tuning", I almost always can get away with quick-n-dirty use of
vmstat and top, and only rarely have to descend into more complex
tools. I'd hate to loose this quick-n-dirty utility, which,
again ... my gut impression is that these numbers suddenly turn
mostly meaningless.
That is, if I run the same task 3 times over the next few hours,
will vmstat/top/ps report more or less he same figures? I'm
concerned that they won't ... that I'll see different values
come out, depending on whether the chip is overheating, or whether
some other partition is stealing, or whatever causes this thing to
dynamically scale.
This begs the question of "what is the real, actual elapsed time?"
... currently, the "real time" depends very much on how often your
process got scheduled -- but, if your process is scheduled but
(due to scaling) isn't "actually running", should that count towards
the "real time"?
---
I supose that its inevitable that this stuff will get more complex;
I'm just trying to make sure we don't end up doing this backwards,
and deciding to change it around later.
I already notice that "stolen time" is causing confusion in some
areas. Its disconcerting to have lots of cores, and lots of threads
per core, only to find that some of your time has been "stolen".
I'm still wondering ... was this the right way to report this?
--linas
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