On Thu, 02 Jun 2005 08:26:46 -0400
jamal <hadi@xxxxxxxxxx> wrote:
> On Tue, 2005-31-05 at 18:28 -0500, Jon Mason wrote:
> > On Tuesday 31 May 2005 05:14 pm, David S. Miller wrote:
> > > From: Jon Mason <jdmason@xxxxxxxxxx>
> > > Date: Tue, 31 May 2005 17:07:54 -0500
> > >
> > > > Of course some performace analysis would have to be done to determine
> > > > the
> > > > optimal numbers for each speed/duplexity setting per driver.
> > >
> > > per cpu speed, per memory bus speed, per I/O bus speed, and add in other
> > > complications such as NUMA
> > >
> > > My point is that whatever experimental number you come up with will be
> > > good for that driver on your systems, not necessarily for others.
> > >
> > > Even within a system, whatever number you select will be the wrong
> > > thing to use if one starts a continuous I/O stream to the SATA
> > > controller in the next PCI slot, for example.
> > >
> > > We keep getting bitten by this, as the Altix perf data continually shows,
> > > and we need to absolutely stop thinking this way.
> > >
> > > The way to go is to make selections based upon observed events and
> > > mesaurements.
> >
> > I'm not arguing against a /proc entry to tune dev->weight for those
> > sysadmins
> > advanced enough to do that. I am arguing that we can make the driver
> > smarter
> > (at little/no cost) for "out of the box" users.
> >
>
> What is the point of making the driver "smarter"?
> Recall, the algorithm used to schedule the netdevices is based on an
> extension of Weighted Round Robin from Varghese et al known as DRR (ask
> gooogle for details).
> The idea is to provide fairness amongst many drivers. As an example, if
> you have a gige driver it shouldnt be taking all the resources at the
> expense of starving the fastether driver.
> If the admin wants one driver to be more "important" than the other,
> s/he will make sure it has a higher weight.
>
In fact, since the default weighting should be based on the amount of cpu time
expended
per frame rather than link speed. The point is that a more "heavy weight"
driver shouldn't
starve out all the others.
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