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SubjectRe: Scheduler fairness problem on 2.6 series (Attn: Nick Piggin and others)
Peter Williams wrote:
> Peter Williams wrote:
>> Peter Williams wrote:
>>> William Lee Irwin III wrote:
>>>> On Tue, Aug 10, 2004 at 07:21:43PM -0700, 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 Williams

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

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