Re: Scheduler fairness problem on 2.6 series (Attn: Nick Piggin and others)

[Con Kolivas]

Peter Williams writes:

> Peter Williams wrote:
> > Peter Williams wrote:
> >
> > > William Lee Irwin III wrote:
> > >
> > > > On Tue, Aug 10, 2004 at 07:21:43PM -0700, spaminos-ker@xxxxxxxxx wrote:
> > > >
> > > > > I am not very familiar with all the parameters, so I just kept the 
> > > > > defaults
> > > > > Anything else I could try?
> > > > > Nicolas
> > > >
> > > >
> > > >
> > > >
> > > > No. It appeared that the SPA bits had sufficient fairness in them to
> > > > pass this test but apparently not quite enough.
> > >
> > > The interactive bonus may interfere with fairness (the throughput 
> > > bonus should actually help it for tasks with equal nice) so you could 
> > > try setting max_ia_bonus to zero (and possibly increasing 
> > > max_tpt_bonus). With "eb" mode this should still give good interactive 
> > > response but expect interactive response to suffer a little in "pb" 
> > > mode however renicing the X server to a negative value should help.
> >
> >
> > I should also have mentioned that fiddling with the promotion interval 
> > may help.
>
> Having reread your original e-mail I think that this problem is probably 
>   being caused by the interactive bonus mechanism classifying the httpd 
> server threads as "interactive" threads and giving them a bonus.  But 
> for some reason the daemon is not identified as "interactive" meaning 
> that it gets given a lower priority.  In this situation if there's a 
> large number of httpd threads (even with promotion) it could take quite 
> a while for the daemon to get a look in.  Without promotion total 
> starvation is even a possibility.
>
> Peter
> PS For both "eb" and "pb" modes, max_io_bonus should be set to zero on 
> servers (where interactive responsiveness isn't an issue).
> PPS For "sc" mode, try setting "interactive" to zero and "compute" to 1.

No, compute should not be set to 1 for a server. It is reserved only for 
computational nodes, not regular servers. "Compute"  will increase latency 
which is undersirable.

Cheers,
Con

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