lkml.org 
[lkml]   [2004]   [Oct]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8
    On Thu, Oct 21 2004, Thomas Gleixner wrote:
    > On Thu, 2004-10-21 at 22:38, Bill Huey wrote:
    > > 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.
    > >
    >
    > Hey, let's stop this here.
    >
    > You are both (in)correct :)
    >
    > 1. It makes no sense to discuss, why X has been considered correct for
    > time T.

    Because it is correct. Debating that it's now incorrect because it
    inconveniently happens to make some detection scheme harder is silly.

    > 2. Counted semaphores are a valid use and should be marked explicit as
    > counted semaphores.

    Indeed

    > 3. Using mutexes and semaphores for event and completion signalling
    > should be converted to the appropriate interfaces.

    Agree. Do you test all your conversions? Whole-sale conversions like
    this tend to break at least some of the drivers. And that's totally
    unacceptable, breaking a working solution because of something that's
    not really a bug.

    > A bunch of work, but not really hard.

    Not if you don't test it.

    --
    Jens Axboe

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 14:07    [W:4.106 / U:0.060 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site