On Thu, May 24, 2012 at 08:33:15AM -0700, Mark Pizzolato - Info Comm wrote:
On Thursday, May 24, 2012, at 7:40 AM, Lennert Van Alboom wrote:
Has anyone managed to get cpu idle detection working on FreeBSD (9.0-
RELEASE)?
Whenever I try to set the idle option, I get the following:
vax.ini.autostart> SET CPU IDLE
Command not allowed
vax.ini.autostart> SET CPU IDLE=VMS
Command not allowed
Same happens with the other options (Ultrix, OpenBSD, ...).
I tried upgrading to SIMH 3.9.0, but that didn't change anything. And I can't
have SIMH eat a full core nonstop... :-)
The concept of CPU idling depends on the simulator being able to sleep with sufficiently
small granularity that events in the simulated system 'seem' to happen at the normally
expected times. The key one here is the simulated clock tick. The simulated VAX has a
clock tick of 10ms. Idling works well when the host OS can sleep with granularity
smaller than 10ms. It can still work if the host OS can sleep with granularity of 10ms,
but the simulated OS will probably see significant clock drift. If the host OS can't
sleep with granularity of 10ms or less, then simh doesn't offer idling and you see the
"command not allowed" response. The granularity which is needed is NOT the
units which can be specified in a call to nanosleep(or some other mechanism), but the
actual amount of wall clock time which elapses when a call to sleep(1ms) is executed.
The idle initialization code in SIMH 3.9-0 explicitly attempts a number of such sleep
operations and uses the measured elapsed tim
e to determine the host's sleep resolution value. Using simh 3.9-0 you should
be able to determine the value which was measured by:
sim> SHOW -D THROT
Throttling disabled
Wait rate = 1 ms
sim>
Aha. A clue appears :-) however, when trying this:
VAX simulator V3.9-0
sim> SHOW -D THROT
Throttling not available
So I guess there's something more fundamental not working here... that error
seems to originate from sim_idle_rate_ms being zero, but I don't know the code
well enough to see what that means.
Some OS environments (windows) allow user mode programs to dynamically change
the OS clock tick size (down to 1ms). On windows, simh leverages this
capability. Most other OS environments don't allow any dynamic changing of the
host tick size, but they may provide boot time or other ways to influence the
kernel's tick size. How you do this on any particular platform is up to you.
If you find a way to do this for FreeBSD (9.0-RELEASE), let the list know so
others may benefit in the future....
Will do, if I ever figure this out...
Thanks,
Lennert
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