Con Kolivas wrote:
On Monday 20 February 2006 16:02, Peter Williams wrote:
[snip description]
Hi peter, I've had a good look and have just a couple of comments:
---
#endif
int prio, static_prio;
+#ifdef CONFIG_SMP
+ int load_weight; /* for load balancing purposes */
+#endif
---
Can this be moved up to be part of the other ifdef CONFIG_SMP? Not highly
significant since it's in a .h file but looks a tiny bit nicer.
I originally put it where it is to be near prio and static_prio which
are referenced at the same time as it BUT that doesn't happen often
enough to justify it anymore so I guess it can be moved.
---
+/*
+ * Priority weight for load balancing ranges from 1/20 (nice==19) to 459/20
(RT
+ * priority of 100).
+ */
+#define NICE_TO_LOAD_PRIO(nice) \
+ ((nice >= 0) ? (20 - (nice)) : (20 + (nice) * (nice)))
+#define LOAD_WEIGHT(lp) \
+ (((lp) * SCHED_LOAD_SCALE) / NICE_TO_LOAD_PRIO(0))
+#define NICE_TO_LOAD_WEIGHT(nice) LOAD_WEIGHT(NICE_TO_LOAD_PRIO(nice))
+#define PRIO_TO_LOAD_WEIGHT(prio)
NICE_TO_LOAD_WEIGHT(PRIO_TO_NICE(prio))
+#define RTPRIO_TO_LOAD_WEIGHT(rp) \
+ LOAD_WEIGHT(NICE_TO_LOAD_PRIO(-20) + (rp))
---
The weighting seems not related to anything in particular apart from saying
that -nice values are more heavily weighted.
The idea (for the change from the earlier model) was to actually give
equal weight to negative and positive nices. Under the old (purely
linear) model a nice=19 task has 1/20th the weight of a nice==0 task but
a nice==-20 task only has twice the weight of a nice==0 so that system
is heavily weighted against negative nices. With this new mapping a
nice=19 has 1/20th and a nice==-19 has 20 times the weight of a nice==0
task and to me that is symmetric. Does that make sense to you?
Should I add a comment to explain the mapping?
Since you only do this when
setting the priority of tasks can you link it to the scale of (SCHED_NORMAL)
tasks' timeslice instead even though that will take a fraction more
calculation? RTPRIO_TO_LOAD_WEIGHT is fine since there isn't any obvious cpu
proportion relationship to rt_prio level.
Interesting idea. I'll look at this more closely.
Otherwise, good work, thanks!
Signed-off-by: Peter Williams <[email protected]>
Signed-off-by: Con Kolivas <[email protected]>
Cheers,
Con
Peter
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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