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

[Con Kolivas <kernel@kolivas.org>]

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@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.

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