Andrew Morton wrote:
If the task can exceed its cap without impacting any other tasks (ie: there
is spare idle capacity), what happens? I trust that spare capacity gets
used?
As I said in another reply, the answer to this is yes for soft caps and
how good a job was demonstrated by the kernbench results that I
included. Repeated here:
Average Optimal -j 8 Load Run:
Vanilla Patch Applied Soft Cap 0%
Elapsed Time 1056.1 (1.92) 1048.2 (0.62) 1064.1 (1.59)
User Time 1908.1 (1.09) 1895.2 (1.30) 1926.6 (1.39)
System Time 181.7 (0.60) 177.5 (0.74) 173.8 (1.07)
Total 2089.8 2072.7 2100.4
Percent CPU 197.6 (0.55) 197.0 (0) 197.0 (0)
Context Switches 49253.6 (136.31) 48881.4 (92.03) 92490.8 (163.71)
Sleeps 28038.8 (228.11) 28136.0 (250.65) 25769.4 (280.40)
Note that the (slight) increase in the elapsed time when using a soft
cap of zero can be directly attributed to the increase in CPU usage due
to the cap overhead (an approximate increase of 16 seconds for elapsed
time with an approximate increase of 28 seconds (for two CPUs) in CPU
time consumed when comparing the "patch applied" and "soft cap 0%" numbers).
I think this illustrates that (for soft caps) spare capacity is not wasted?
> (Is this termed "work conserving"?)
I don't know but it sounds apt.
Peter
PS For ordinary users, I think that the ability to run jobs in the
background by using a soft cap of zero is the most useful thing that
this patch provides.
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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