Re: [ANNOUNCE][RFC] PlugSched-6.2 for 2.6.16-rc1 and 2.6.16-rc1-mm1

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

Peter Williams wrote:
> Paolo Ornati wrote:
> 
>> On Fri, 20 Jan 2006 08:45:43 +1100
>> Peter Williams <pwil3058@bigpond.net.au> wrote:
>>
>>
>>> Modifications have been made to spa_ws to (hopefully) address the 
>>> issues raised by Paolo Ornati recently and a new entitlement based 
>>> interpretation of "nice" scheduler, spa_ebs, which is a cut down 
>>> version of the Zaphod schedulers "eb" mode has been added as this 
>>> mode of Zaphod performed will for Paolo's problem when he tried it at 
>>> my request. Paolo, could you please give these a test drive on your 
>>> problem?
>>
>>
>>
>> ---- spa_ws: the problem is still here
>>
>> (sched_fooler)
>> ./a.out 3000 & ./a.out 4307 &
>>
>>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>>  5573 paolo     34   0  2396  292  228 R 59.0  0.1   0:24.51 a.out
>>  5572 paolo     34   0  2392  288  228 R 40.7  0.1   0:16.94 a.out
>>  5580 paolo     35   0  4948 1468  372 R  0.3  0.3   0:00.04 dd
>>
>>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>>  5573 paolo     34   0  2396  292  228 R 59.3  0.1   0:59.65 a.out
>>  5572 paolo     33   0  2392  288  228 R 40.3  0.1   0:41.32 a.out
>>  5440 paolo     28   0 86652  21m  15m S  0.3  4.4   0:03.34 konsole
>>  5580 paolo     37   0  4948 1468  372 R  0.3  0.3   0:00.10 dd
>>
>>
>> (real life - transcode)
>>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>>  5585 paolo     33   0  115m  18m 2432 S 90.0  3.7   0:38.04 transcode
>>  5599 paolo     37   0 50996 4472 1872 R  9.1  0.9   0:04.03 tcdecode
>>  5610 paolo     37   0  4948 1468  372 R  0.6  0.3   0:00.19 dd
>>
>>
>> DD test takes ages in both cases.
>>
>> What exactly have you done to spa_ws?
> 
> 
> I added a "nice aware" version of the throughput bonuses from spa_svr 
> and renamed them fairness bonus.  They don't appear to be working :-(
> 
> 34 is the priority value that ordinary tasks should end up with i.e. if 
> they don't look like interactive tasks or CPU hogs.  If they look like 
> interactive tasks they should get a lower one via the interactive bonus 
> mechanism and if they look like CPU hogs they should get a higher one 
> via the same mechanism.  In addition to this tasks will get bonuses if 
> they seem to be being treated unfairly i.e. spending too much time on 
> run queues waiting for CPU access.
> 
> Looking at your numbers the transcode task has the priority that I'd 
> expect it to have but tcdecode and dd seem to have had their priorities 
> adjusted in the wrong direction.   It's almost like they'd been 
> (incorrectly, obviously) identified as CPU hogs :-(.  I'll look into this.

I forgot that I'd also made changes to the "CPU hog" component of the 
interactive response as the one I had was useless on heavily loaded 
systems.  It appears that I made a mistake (I used interactive 
sleepiness instead of ordinary sleepiness for detecting CPU hogs) during 
these changes which means that tasks that do no interactive sleeping 
(such as your dd) get classified as CPU hogs.  The transcode task 
escapes this because, although its sleeps aren't really interactive, 
they're classified as such.  More widespread us of TASK_NONINTERACTIVE 
would fix this but would need to be done carefully as it would risk 
breaking the normal scheduler.

However, in spite of the above, the fairness mechanism should have been 
able to generate enough bonus points to get dd's priority back to less 
than 34.  I'm still investigating why this didn't happen.

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

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