[gentoo-amd64] Re: sys-kernel/ck-sources

[Duncan]

tomas posted <435D5011.6080506@××××××.lt>, excerpted below,  on Mon, 24
Oct 2005 21:20:17 +0000:

> What is the difference between gentoo-sources and:
> *  sys-kernel/ck-sources
>       Latest version available: 2.6.13_p8
>       Latest version installed: [ Not Installed ]
>       Size of downloaded files: 37,599 kB
>       Homepage:    http://members.optusnet.com.au/ckolivas/kernel/
>       Description: Full sources for the Linux kernel with Con Kolivas'
> high performance patchset and Gentoo's basic patchset.
>       License:     GPL-2
>
> and is there any way to make my gentoo work faster? for example encoding
> dvd?

The CK sources have a lot of work specifically designed to lower latency. 
Thus, they are popular with real-time and media production folks, where
certain things need to occur within a specified time.

There is a tradeoff, however, between latency and thruput.  Generally
speaking, one way to decrease latency is to break up large tasks into a
bunch of smaller tasks, doing only one or a few of the smaller tasks at
once, before checking to see if something else needs done.  The problem is
that each task switch requires some bit of overhead, some tiny bit of time
just to do the task switch.  Thus, it's possible to break tasks small
enough that most of the time is spent changing tasks, rather than actually
doing them.

Analogy:  Suppose you have two tasks to do in your eight hour work day. 
You can do each until it's done, then switch to the next, and it might
take you seven hours, because you always know where in the task you are.
You can take an hour lunch or knock off an hour early.  However, if one of
those tasks is something that you have to check every half hour, and spend
five minutes working on it before going back to the other task you were
working on, each time you go back to that other task, you have to remember
where you were and find your place again, which might take you three to
five minutes. Instead of getting done in 7 hours and having that hour
free, you could now be working after quitting time, still trying to
finish, because of all the time spent finding your place after each
interruption.

So... low latency generally means a more responsive system under heavy
load... no freezing mouse syndrome... but the computer will probably take
longer to finish what you give it to do... similar to a speed grade or two
reduction.

One way around the issue, the way I've taken, is a dual-CPU (or now, dual
core) system.  You can then tolerate normal latency settings, or even
higher than normal latency settings, without affecting responsivenes,
because even when both CPUs are heavily loaded, one or the other will get
around to processing the latest mouse movement or sound processing in an
average of half the time it would otherwise ordinarily take.  For system
responsiveness  while encoding DVD or the like, a dual-CPU or dual-core
system is really the way to go.  I've been *MORE* than happy with my
decision to go dual Opteron, shortly after the Opterons came out.  Now,
the same thing is cheaper, doing with single-CPU dual-core, therefore far
cheaper and less complex motherboards (I paid over $400 for my dual CPU
mobo, dual-core compatible single socket boards are now under $100), what 
I did with dual CPU a couple years ago.  I don't expect I'll ever go back
to single core/CPU, so it's a good thing they are going dual-core now. 

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman in
http://www.linuxdevcenter.com/pub/a/linux/2004/12/22/rms_interview.html


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