[vserver] question about scheduling

From: Jeffrey 'jf' Lim <jfs.world_at_gmail.com>
Date: Wed 06 May 2009 - 11:14:50 BST
Message-ID: <4b3125cc0905060314k3f3e951en9e42e848a0939f9e@mail.gmail.com>

hey guys, I'm looking at http://linux-vserver.org/CPU_Scheduler, and
specifically at the "Fair Share" section
(http://linux-vserver.org/CPU_Scheduler#Fair_Share), and i'm a bit

The way the calculation works, it seems like "1/2" and "1/4" isnt
exactly right for the wasted cpu time? It looks more like "1/2 over
(1/2 + 1/4)" vs "1/4 over (1/2 + 1/4)" of the waste cpu time. Is this
intentional? This is a different concept from the "standard" cpu
scheduling, which is a "pure fraction of 1" ("hard limit").

A few other questions:

- the most basic one: how do i define guaranteed + fair share
scheduling for a context? like eg. guarantee of 1/5 for a context, +
1/2 for fair scheduling. I'm looking at the flower page, and while I
know what file to edit for guaranteed cpu, i dont know its format. Is
it simply '1/5'? How about for fair scheduling? Where do i put this?

- is the fair scheduling ratio "dynamic"? Let's say I have 4 contexts.
All of them have Rk/Tk 1/4. And let's suppose that right now, 3
contexts are idle - and only 1 context is busy. So will the wasted cpu
time all go to this one busy context? (ie. '1/4 over 1/4'). Or is it
more like '1/4 over (1/4 + 1/4 + 1/4 + 1/4)'?

- how does this whole bucket token thing work? ie. is it a
"sub-scheduler" within the standard kernel scheduler (kernel schedules
vserver process, vserver process then schedules context). Or is it an
entire "takeover/replacement" of the standard kernel scheduler?

- any recommended number for "amount of tokens on start"? Let's say I
dont want any penalization (and therefore minimum tokens = 0). And I
want scheduling to be as smooth as possible. Then the recommended
amount would be either 0, or fill rate? I guess this also means that i
am asking a question about the scheduling algorithm. Does it mean that
if a context has let's say 1000 tokens, that the scheduler will let it
use up all its tokens (if it's that busy!) before moving on to another

- any recommended number for maximum number of tokens? again, if i
want smooth scheduling, it looks like putting the fill interval value
here would be right.


In the meantime, here is your PSA:
"It's so hard to write a graphics driver that open-sourcing it would not help."
    -- Andrew Fear, Software Product Manager, NVIDIA Corporation
Received on Wed May 6 11:15:09 2009
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