SCHED_ULE should not be the default

[Mike Tancsa]

On 12/13/2011 7:01 PM, mdf at freebsd.org wrote:
> 
> Has anyone experiencing problems tried to set sysctl kern.sched.steal_thresh=1 ?
> 
> I don't remember what our specific problem at $WORK was, perhaps it
> was just interrupt threads not getting serviced fast enough, but we've
> hard-coded this to 1 and removed the code that sets it in
> sched_initticks().  The same effect should be had by setting the
> sysctl after a box is up.

FWIW, this does impact the performance of pbzip2 on an i7. Using a 1.1G file

pbzip2 -v -c big > /dev/null

with burnP6 running in the background,

sysctl kern.sched.steal_thresh=1 
vs
sysctl kern.sched.steal_thresh=3



    N           Min           Max        Median           Avg        Stddev
x  10     38.005022      38.42238     38.194648     38.165052    0.15546188
+   9     38.695417     40.595544     39.392127     39.435384    0.59814114
Difference at 95.0% confidence
        1.27033 +/- 0.412636
        3.32852% +/- 1.08119%
        (Student's t, pooled s = 0.425627)

a value of 1 is *slightly* faster.


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Mike Tancsa, tel +1 519 651 3400
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