Siddha, Suresh B wrote:
more issues with smpnice patch...
a) consider a 4-way system (simple SMP system with no HT and cores) scenario
where a high priority task (nice -20) is running on P0 and two normal
priority tasks running on P1. load balance with smp nice code
will never be able to detect an imbalance and hence will never move one of
the normal priority tasks on P1 to idle cpus P2 or P3.
Why?
b) smpnice seems to break this patch..
[PATCH] sched: allow the load to grow upto its cpu_power
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=0c117f1b4d14380baeed9c883f765ee023da8761
example scenario for this case: consider a numa system with two nodes, each
node containing four processors. if there are two processes in node-0 and with
node-1 being completely idle, your patch will move one of those processes to
node-1 whereas the previous behavior will retain those two processes in node-0..
(in this case, in your code max_load will be less than busiest_load_per_task)
smpnice patch has complicated the load balance code... Very difficult
to comprehend the side effects of this patch in the presence of different
priority tasks...
That is NOT true. Without smpnice whether the "right thing" happens
with non zero nice tasks is largely down to luck. With smpnice the
result is far more predictable.
The PURPOSE of smpnice IS to alter load balancing in the face of the use
of non zero nice tasks. The reason for doing this is so that nice
reliably effects the allocation of CPU resources on SMP machines. I.e.
changes in load balancing behaviour as a result of tasks having nice
values other than zero is the desired result and NOT a side effect.
Peter
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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