Robert Watson wrote:
On Sun, 22 Feb 2009, Maxim Sobolev wrote:
Hi Jeff,
I have a single-CPU system with P4 HTT-enabled processor
(7.1-RELEASE-p3), kernel compiled with SCHED_ULE.
This is because machdep.hlt_logical_cpus doesn't do what you think it
does. It causes HTT cores to invoke the hlt instruction in their idle
Hmm, as the subject says I am actually talking about flipping
machdep.hyperthreading_allowed, not machdep.hlt_logical_cpus sysctl
here. I provided current value of the latter only to simplify diagnosis
and had not changed it from the default value. AFAIK, the
machdep.hyperthreading_allowed is designed to prevent logical cores from
running any code, works just fine with 6.x/SCHED_4BSD.
Below are screenshots from the dual-core 6.2 system with 4BSD. As you
can easily see, after flipping machdep.hyperthreading_allowed only cores
0 and 2 run actual code, so that it's definitely regression of ULE/7.x:
machdep.hyperthreading_allowed=1:
top: http://sobomax.sippysoft.com/~sobomax/ScreenShot462.png
machdep.hyperthreading_allowed=0:
top: http://sobomax.sippysoft.com/~sobomax/ScreenShot463.png
IMHO, at the very least, if SCHED_ULE doesn't support
machdep.hyperthreading_allowed properly, then when that scheduler is
selected the sysctl should return ENOTSUP or something like this.
-Maxim
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