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

[Peter Williams]

Peter Williams wrote:
> 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.

I've just run your tests on my desktop and with max_ia_bonus at its 
default value I see the "delta = 3" with 20 threads BUT when I set 
max_ia_bonus to zero they stop (in both "eb" and "pb" mode).  So I then 
reran the tests with 60 threads and zero max_ia_bonus and no output was 
generated by your testdelay script in either "eb" or "pb" modes.  I 
didn't try "sc" mode as I have a ZAPHOD kernel loaded (not HYDRA) but 
Con has reported that the problem is absent in his latest patches so 
I'll update the "sc" mode in HYDRA to those patches.

Peter
--
Peter Williams                                   pwil3058@xxxxxxxxxxxxxx

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce

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