[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20071001190932.GA9302@elte.hu>
Date: Mon, 1 Oct 2007 21:09:33 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Chris Friesen <cfriesen@...tel.com>
Cc: Jarek Poplawski <jarkao2@...pl>,
Nick Piggin <nickpiggin@...oo.com.au>,
David Schwartz <davids@...master.com>,
linux-kernel@...r.kernel.org, Mike Galbraith <efault@....de>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Martin Michlmayr <tbm@...ius.com>,
Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
Stephen Hemminger <shemminger@...ux-foundation.org>
Subject: Re: iperf yield usage
* Chris Friesen <cfriesen@...tel.com> wrote:
> >See the background and answers to that in:
> >
> > http://lkml.org/lkml/2007/9/19/357
> > http://lkml.org/lkml/2007/9/19/328
> >
> >there's plenty of recourse possible to all possible kinds of apps.
> >Tune the sysctl flag in one direction or another, depending on which
> >behavior the app is expecting.
>
> Yeah, I read those threads.
>
> It seems like the fundamental source of the disconnect is that the
> tasks used to be sorted by priority (thus making it easy to bump a
> yielding task to the end of that priority level) while now they're
> organized by time (making it harder to do anything priority-based).
> Do I have that right?
not really - the old yield implementation in essence gave the task a
time hit too, because we rotated through tasks based on timeslices. But
the old one requeued yield-ing tasks to the 'active array', and the
decision whether a task is in the active or in the expired array was a
totally stohastic, load-dependent thing. As a result, certain tasks,
under certain workloads saw a "stronger" yield, other tasks saw a
"weaker" yield. (The reason for that implementation was simple: yield
was (and is) unimportant and it was implemented in the most
straightforward way that caused no overhead anywhere else in the
scheduler.)
( and to keep perspective it's also important to correct the subject
line here: it's not about "network slowdown" - nothing in networking
slowed down in any way - it was that iperf used yield in a horrible
way. I changed the subject line to reflect that. )
Ingo
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists