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Date:      Tue, 8 Jul 2003 22:22:07 +1000 (EST)
From:      Andy Farkas <andyf@speednet.com.au>
To:        Terry Lambert <tlambert2@mindspring.com>
Cc:        Dan Nelson <dnelson@allantgroup.com>
Subject:   Re: whats going on with the scheduler?
Message-ID:  <20030708215553.F8850-100000@hewey.af.speednet.com.au>
In-Reply-To: <3F0AA444.28EC5A8E@mindspring.com>

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On Tue, 8 Jul 2003, Terry Lambert wrote:
> Dan Nelson wrote:
> > In the last episode (Jul 08), Andy Farkas said:
> > > If setiathome is making lots of syscalls, then running the 3 instanses
> > > should already show a problem, no?
> >
> > Not if it's ssh that's holding Giant for longer than it should.   The
> > setiathome processes may be calling some really fast syscall 500 times
> > a second which doesn't cause a problem until ssh comes along and calls
> > some other syscall that takes .1 ms to return but also locks Giant long
> > enough to cause the other processes to all back up behind it.
>
> Specifically, if it's sleeping with Giant held because the
> Send-Q is full (use netstat to check) it could block things
> for a long time, waiting for the queue to drain.

scp was retrieving a file, not sending, and it was bandwidth limited.

Any other ideas? Why would 3 (niced) cpu intensive processes suddenly get
reduced cpu time (on a 4 cpu system) when a 4th non-resource intensive
process gets started?


Also, from something that BDE said once, this command will produce
unexpected results when run for more than a few hours:

 for i in `jot -n -s ' ' 20 0 19 1`
 do
    nice -$i sh -c "while :; do echo -n;done" &
 done


--

 :{ andyf@speednet.com.au

        Andy Farkas
    System Administrator
   Speednet Communications
 http://www.speednet.com.au/






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