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SubjectRe: [patch] lowlatency patch for 2.4, lowlatency-2.4.0-test6-B5
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On Fri, 04 Aug 2000, Rogier Wolff wrote:
> Andrew Morton wrote:
> > - There's some device driver module which takes ~100 millisecs when it's
> > loaded (Benno has details). Leave it alone - we can't and shouldn't audit all
> > the device driver initialisation code.
>
> I haven't checked this, but I bet there are a few drivers that I've
> written that are a lot worse in this respect. I hope that this isn't a
> real problem for anyone? Don't use modules if it bothers you, or load
> the modules at boot, and make sure they don't unload.

I agree here, module loading is not a problem because if you plan to
do low-latency stuff. (because you can load all at boot time)

I do not know what happens in the module unloading case.
(potentially similar problems).

The user has to make sure that his distro does not unload the modules
when they are unused for longer time.

Any anyone write a short summary how the various distros behave in this
respect. (do they use automatic unloading yes/no ? )

I'm interested mainly in Redhat, Suse , Debian and Mandrake (and perhaps
others)

PS: the opening of raw devices was mentioned to be a potential problem:

But what if a HD recording app wants to use the raw disk partition rather than
a file, will this cause a latency peak at the open/close of the device ?

Last question: is there a way to access a 10GB partion from userspace via
open() , lseek() , read()/write() calls ?

The problem is the 32bit offset limitation (2GB) , will this be possible using
lseek64() , read64() etc ?

Is this already possible on kernel 2.2 or will this be a 2.4 feature.

If the latter is true, what was the method to access to large disk
partitions from userspace ?


thanks,
Benno.


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