I'd like to clarify that I'm not trying to push this particular code to
the kernel. I'm a researcher. My intent was to point out that we have a
problem in the scheduler and my dwrr algorithm can potentially help fix
it. The patch itself was merely a proof-of-concept. I'd be thrilled if the
algorithm can be proven useful in the real world. I appreciate the people
who have given me comments. Since then, I've revised my algorithm/code.
Now it doesn't require global locking but retains strong fairness
properties (which I was able to prove mathematically).
Thank you,
tong
On Thu, 26 Jul 2007, Li, Tong N wrote:
On Thu, 2007-07-26 at 23:31 +0200, Ingo Molnar wrote:
* Tong Li <[EMAIL PROTECTED]> wrote:
you need to measure it over longer periods of time. Its not worth
balancing for such a thing in any high-frequency manner. (we'd trash
the cache constantly migrating tasks back and forth.)
I have some data below, but before that, I'd like to say, at the same
load balancing rate, my proposed approach would allow us to have
fairness on the order of seconds. I'm less concerned about trashing
the cache. The important thing is to have a knob that allow users to
trade off fairness and performance based on their needs. [...]
such a knob already exists to a certain degree, but i havent tested its
full effects on SMP fairness yet. If you pull my scheduler tree:
git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched.git
and if you enable CONFIG_SCHED_DEBUG, then all the sched-domain
parameters become runtime tunable under /proc/sys/cpu*.
Could you try to increase the cross-CPU rebalancing frequency and see
how it impacts the precision of your measurement? Tune 'min_interval'
and 'max_interval' down to increase the frequency of rebalancing.
Ingo
Yes, I'll do it when I find time. If anyone is willing to do the
testing, please let me know and I can post my benchmark. On the other
hand, I don't think tuning the existing knobs will help solve the
problem. The root of the problem is that the current load balancing
doesn't take into account how much time each task has been running and
how much it's entitled. This is why I'm proposing a new approach for
solving it. The new approach, as I said, will be much more fair/accurate
than the current one even without tuning those balancing intervals
(i.e., it's able to provide good fairness even if balancing is less
frequent).
tong
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