Re: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8

[hui]

On Thu, Oct 21, 2004 at 10:33:50PM +0200, Jens Axboe wrote:
> On Thu, Oct 21 2004, Bill Huey wrote:
> > You use a semaphore to protect data, a completion isn't protecting data
> > but preserving a certain kind of wait ordering in the code. The
> > possibility of overloading the current mutex_t for PI makes for a conceptual
> > mismatch when used in this case since having a kind of priority for
> > completions is a bit odd. It's better to flat out use a completion
> > instead, IMO.
> 
> Linux semaphores (being counted) have always been a fine fit for things
> like the loop use, where you get to down it 10 times because you have 10
> items pending. I know this isn't the traditional mutex and that it
> doesn't protect data as such, but is was never abuse. It isn't overload.
> Doing it with a traditional mutex (I'm assuming this is what mutex_t is
> in Ingos tree) would be overload and a bad idea, indeed.

Well, this is something that's got to be considered by the larger Linux
community and whether these conventions are to be kept or removed. It's
a larger issue than what can be address in Ingo's preemption patch, but
with inevitable need for something like this in the kernel (hard RT)
it's really unavoidable collision. IMO, it's got to go, which is a nasty
change.

bill

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