On Sat, Nov 17, 2007 at 05:43:33AM +1030, David Newall wrote:
> There are a couple of points I would make about your python test harness.
> Your program compares real+system jiffies for both cpus; an ideal result
> would be 1.00. The measurement is taken over a relatively short period of
> approximately a half-second, and you kill the CPU hogs before taking final
> measurements, even wait for them to die first. You repeat this
> measurement, starting and killing CPU hogs each time. Why do you do that?
The Python test harness is fairly artificial, but this is just the
best way I found to reliably reproduce the problem in a short amount
of time. It was just for convenience while running git-bisect. When
running the C program directly, there seems to be a somewhat random
chance that it will start up in the "bad" state. Once the single CPU
is stuck in this mostly-idle mode, it seems to stay that way for a
while.
> What happens if you start the hogs and take the baseline outside of the
> loop?
The problem still occurs then, but killing/restarting the test app
seems to trigger the problem more reliably. As I said in the original
email about this, left to its own devices this problem will occur
seemingly-randomly. In the original VMware code I observed this
problem in, the same process would flip between the "good" and "bad"
states seemingly randomly, every few seconds.
Thanks,
--Micah
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