Re: [OKS] O(1) scheduler in 2.4

[J Sloan <joe@tmsusa.com>]

Ingo, it's apparent you are refraining from
pushing this O(1) scheduler - that's admirable,
but don't swing too far in the other direction.

The fact is, it's working well in 2.5, it's working
well in the 2.4-ac tree, it's working well in the
2.4-aa tree, and Red Hat has been shipping it.

It will soon be the case that most Linux users
are using O(1) - thus any poor clown who
downloads the standard src from kernel.org
has a large task ahead of him if he wants
similar functionality to the majority of
linux users. This divergence may not be a
good thing...

;-)

Joe

Ingo Molnar wrote:

>On Wed, 3 Jul 2002, Bill Davidsen wrote:
>
>  
>
>>>it might be a candidate for inclusion once it has _proven_ stability and
>>>robustness (in terms of tester and developer exposion), on the same order
>>>of magnitude as the 2.4 kernel - but that needs time and exposure in trees
>>>like the -ac tree and vendor trees. It might not happen at all, during the
>>>lifetime of 2.4.
>>>      
>>>
>>It has already proven to be stable and robust in the sense that it isn't
>>worse than the stock scheduler on typical loads and is vastly better on
>>some.
>>    
>>
>
>this is your experience, and i'm happy about that. Whether it's the same
>experience for 90% of Linux users, time will tell.
>
>  
>
>>>Note that the O(1) scheduler isnt a security or stability fix, neither is
>>>it a driver backport. It isnt a feature backport that enables hardware
>>>that couldnt be used in 2.4 before. The VM was a special case because most
>>>people agreed that it truly sucked, and even though people keep
>>>disagreeing about that decision, the VM is in a pretty good shape now -
>>>and we still have good correlation between the VM in 2.5, and the VM in
>>>2.4. The 2.4 scheduler on the other hand doesnt suck for 99% of the
>>>people, so our hands are not forced in any way - we have the choice of a
>>>'proven-rock-solid good scheduler' vs. an 'even better, but still young
>>>scheduler'.
>>>      
>>>
>>Here I disagree. Sure behaves like a stability fix to me. On a system
>>with a mix of interractive and cpu-bound processes, including processes
>>with hundreds of threads, you just can't get reasonable performance
>>balancing with nice() because it is totally impractical to keep tuning a
>>thread which changes from hog to disk io to socket waits with a human in
>>the loop. The new scheduler notices this stuff and makes it work, I
>>don't even know for sure (as in tried it) if you can have different nice
>>on threads of the same process.
>>    
>>
>
>(yes, it's possible to nice() individual threads.)
>
>  
>
>>This is not some neat feature to buy a few percent better this or that,
>>this is roughly 50% more users on the server before it falls over, and
>>no total bogs when many threads change to hog mode at once.
>>    
>>
>
>are these hard numbers? I havent seen much hard data yet from real-life
>servers using the O(1) scheduler. There was lots of feedback from
>desktop-class systems that behave better, but servers used to be pretty
>good with the previous scheduler as well.
>
>  
>
>>You will not hear me saying this about preempt, or low-latency, and I
>>bet that after I try lock-break this weekend I won't fell that I have to
>>have that either. The O(1) scheduler is self defense against badly
>>behaved processes, and the reason it should go in mainline is so it
>>won't depend on someone finding the time to backport the fun stuff from
>>2.5 as a patch every time.
>>    
>>
>
>well, the O(1) scheduler indeed tries to put up as much defense against
>'badly behaved' processes as possible. In fact you should try to start up
>your admin shells via nice -20, that gives much more priority than it used
>to under the previous scheduler - it's very close to the RT priorities,
>but without the risks. This works in the other direction as well: nice +19
>has a much stronger meaning (in terms of preemption and timeslice
>distribution) than it used to.
>
>	Ingo
>
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