linux-kernel - Re: CFS review

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Date:	Fri, 10 Aug 2007 15:52:08 +0200 (CEST)
From:	Roman Zippel <zippel@...ux-m68k.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Mike Galbraith <efault@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: CFS review

Hi,

On Fri, 10 Aug 2007, Ingo Molnar wrote:

> > I disabled the jiffies logic and the result is still the same, so this 
> > problem isn't related to resolution at all.
> 
> how did you disable the jiffies logic?

I commented it out.

> Also, could you please send me 
> the cfs-debug-info.sh:
> 
>   http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh
> 
> captured _while_ the above workload is running. This is the third time 
> i've asked for that :-)

Is there any reason to believe my analysis is wrong?
So far you haven't answered a single question about the CFS design...

Anyway, I give you something better - the raw trace data for 2ms:

1186747669.274790012: update_curr 0xc7fb06f0,479587,319708,21288884188,159880,7360532
1186747669.274790375: dequeue_entity 0xc7fb06f0,21280402988,159880
1186747669.274792580: sched 2848,2846,0xc7432cb0,-7520413
1186747669.274820987: update_curr 0xc7432ce0,29302,-130577,21288913490,1,-7680293
1186747669.274821269: dequeue_entity 0xc7432ce0,21296077409,1
1186747669.274821930: enqueue_entity 0xc7432ce0,21296593783,1
1186747669.274826979: update_curr 0xc7432ce0,5707,5707,21288919197,1,-7680294
1186747669.274827724: enqueue_entity 0xc7432180,21280919197,639451
1186747669.274829948: update_curr 0xc7432ce0,1553,-318172,21288920750,319726,-8000000
1186747669.274831878: sched 2846,2847,0xc7432150,8000000
1186747669.275789883: update_curr 0xc7432180,479797,319935,21289400547,159864,7360339
1186747669.275790295: dequeue_entity 0xc7432180,21280919197,159864
1186747669.275792439: sched 2847,2846,0xc7432cb0,-7520203
1186747669.275820819: update_curr 0xc7432ce0,29238,-130625,21289429785,1,-7680067
1186747669.275821109: dequeue_entity 0xc7432ce0,21296593783,1
1186747669.275821763: enqueue_entity 0xc7432ce0,21297109852,1
1186747669.275826887: update_curr 0xc7432ce0,5772,5772,21289435557,1,-7680068
1186747669.275827652: enqueue_entity 0xc7fb0ca0,21281435557,639881
1186747669.275829826: update_curr 0xc7432ce0,1549,-318391,21289437106,319941,-8000000
1186747669.275831584: sched 2846,2849,0xc7fb0c70,8000000

About the values:

update_curr: sched_entity, delta_fair, delta_mine, fair_clock, sleeper_bonus, wait_runtime
	(final values at the end of __update_curr)
{en,de}queue_entity: sched_entity, fair_key, sleeper_bonus
	(at the start of __enqueue_entity/__dequeue_entity)
sched: prev_pid,pid,current,wait_runtime
	(at the end of scheduling, note that current has a small structure 
	offset to sched_entity)

It starts with a timer task going to sleep, the busy loop runs for a few 
usec until the timer tick, the next timer task is woken up (sleeper_bonus 
is increased). Before switching the tasks, current task is updated and 
it's punished with the sleeper_bonus.

These tests are done without the recent updates, but they don't seem to
change the basic logic. AFAICT the change to __update_curr() only makes it 
more unpredictable, which task is punished with the sleeper_bonus.

So again, what is this logic _supposed_ to do?

bye, Roman
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