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

[Peter Williams <pwil3058@bigpond.net.au>]

spaminos-ker@yahoo.com wrote:
> --- Peter Williams <pwil3058@bigpond.net.au> wrote:
> 
>>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.
>>
> 
> 
> I just tried the same test on spa-zaphod-linux 4.1 over 2.6.8-rc4
> 
> I also have messages with 20 threads "delta = 3" that go away when I set
> max_ia_bonus to 0 (and stay off with 60 threads too) in "pb" mode.

I'm going to do some experiments to measure the relationship between the 
size of max_ia_bonus and the observed delays to see if there's value 
that gives acceptable performance without turning bonuses off completely.

> But, unlike your desktop, the "eb" mode doesn't seem to get better by setting
> max_ia_bonus to 0 on my machine, maybe I need to tweak something else? (even
> though, the idea of tweaking for a given workload doesn't sound very good to
> me).

You could try increasing "base_promotion_interval".  When I have a 
better idea of the best values (for each mode) for the various 
parameters I'll reset their values when the mode is changed.

> 
> The "pb" mode is very responsive with the system under heavy load, I like it :)

That's good to hear.

If you have time, I'd appreciate if you could try a few different values 
of max_ia_bonus to determine the minimum value that still gives good 
responsiveness for your system?  I'm trying to get a feel for how much 
this varies from system to system.

> 
> I will run some tests over the week end with the actual server to see the
> effect of this patch on a more complex system.
> 
> Nicolas
> 
> PS: the machine I am using is a pure server, only accessible through ssh, so I
> can not really tell the behavior under X.

If it's a pure server I imagine that it's not running X.  On a pure 
server I'd recommend setting max_ia_bonus to zero.

Thanks
Peter
-- 
Peter Williams                                   pwil3058@bigpond.net.au

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