Re: scheduler going backwards solution?

[Yuri Pryadkin <yuri@who.isi.edu>]

Xin Wang <xwang@ctr.columbia.edu> writes:

> There were a lot of discussions on "scheduler going backwards" problem
> in this list. I wonder what is the final solution?

I think I can summarize it as follows:

1.  If you see this warning, the first thing you should do is to make
    sure you're using the latest version of scheduler.cc.  If necessary,
    get the latest version from 
	http://www-mash.cs.berkeley.edu/cgi-bin/cvsweb/ns-2/scheduler.cc
    Don't forget to recompile.  If after that you still see this error
    message, please report this to the list.

2.  If the previous didn't work for you, use Heap scheduler instead of
    default Calendar (see Simulator instproc use-scheduler command and
    nsdoc).  Heap scheduler, although a little less effective than
    Calendar, doesn't have a numeric stability problem and should not
    give you this error.  Again, if it does, please report this to the
    list.

> 
> Also, it seemed that most of the discussion were for Calender scheduler.
> I met this problem when I used FQ as scheduler.  It worked fine
> when my link load was 60%. I tried to increase the average rate of each
> flow 10%, then this problem appeared. 
> Any suggestions will be appreciated.


There is only one central scheduler in ns which manages a single queue
of timed events.  It's Calendar by default, but you can switch to
using Heap or List.  FQ is sometimes referred to as a scheduling
algorithm, but in a different sense, it schedules packets arriving at
a node.  If you look at the code in fq.cc, FQ derives from Queue and
not Scheduler.  FQ uses the same centralized scheduler as all other
objects.


 -Yuri

> 
> 
> Xin