lkml.org 
[lkml]   [2008]   [Jun]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: fair group scheduler not so fair?
Srivatsa Vaddagiri wrote:

> That seems to be pretty difficult to achieve with the per-cpu runqueue
> and smpnice based load balancing approach we have now.

Okay, thanks.

>>Initially I tried a simple setup with three hogs all in the default "sys"
>>group. Over multiple retries using 10-sec intervals, sometimes it gave
>>roughly 67% for each task, other times it settled into a 100/50/50 split
>>that remained stable over time.

> Was this with imbalance_pct set to 105? Does it make any difference if
> you change imbalance_pct to say 102?

It was set to 105 initially. I later reproduced the problem with 102.
For example, the following was with 102, with three tasks created in the
sys class. Based on the runtime, pid 2499 has been getting a cpu all to
itself for over a minute.

2499 cfriesen 20 0 3800 392 336 R 99.8 0.0 1:05.85 cat
2496 cfriesen 20 0 3800 392 336 R 50.0 0.0 0:32.95 cat
2498 cfriesen 20 0 3800 392 336 R 50.0 0.0 0:32.97 cat

The next run was much better, with sub-second fairness after a minute.

2505 cfriesen 20 0 3800 392 336 R 68.2 0.0 1:00.32 cat
2506 cfriesen 20 0 3800 392 336 R 66.9 0.0 0:59.85 cat
2503 cfriesen 20 0 3800 392 336 R 64.2 0.0 1:00.21 cat

The lack of predictability is disturbing, as it implies some sensitivity
to the specific test conditions.

>>With three groups, one task in each, I tried both 10 and 60 second
>>intervals. The longer interval looked better but was still up to 0.8% off:
>
>
> I honestly don't know if we can do better than 0.8%! In any case, I'd
> expect that it would require more drastic changes.

No problem. It's still far superior than the SMP performance of CKRM,
which is what we're currently using (although heavily modified).

Chris



\
 
 \ /
  Last update: 2008-06-02 22:05    [from the cache]
©2003-2011 Jasper Spaans