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

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

Peter Williams wrote:
> Peter Williams wrote:
> 
>> William Lee Irwin III wrote:
>>
>>> On Tue, Aug 10, 2004 at 07:21:43PM -0700, spaminos-ker@yahoo.com 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.
-- 
Peter Williams                                   pwil3058@bigpond.net.au

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