lkml.org 
[lkml]   [2008]   [Apr]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] Replace completions with semaphores
    Linus Torvalds wrote:
    >
    > On Tue, 15 Apr 2008, Andi Kleen wrote:
    >>> - probably add support for completions to do counting
    >> But that's just a semaphore, isn't it?
    >
    > Exactly. But the point here is:
    >
    > - nobody should use semaphores anyway (use mutexes)

    For normal locks. But if you have N number of outstanding
    events you need to wait for the semaphore is the right primitive.

    And it seems there is a not high but non trivial number
    of places in the kernel who have a legitimate need for this.

    > - making *more* code use semaphores is wrong
    > - completions have a different _mental_ model
    >
    > IOW, this is not about implementation issues. It's about how you think
    > about the operations.

    Ok so you just want to rename it.

    Fine for me. I always found up() and down() unintuitive anyways
    (but it's admittedly better than "P" and "V" which some other systems use)

    > We should _not_ implement completions as semaphores, simply because we
    > want to get *rid* of semaphores some day.
    >
    > So rather than this long and involved patch series that first makes
    > semaphores generic, and then makes them be used as completions, I'd much
    > rather just skip this whole pointless exercise entirely.
    >
    > Why have "generic semaphores" at all, if we want to get rid of them?

    Because we still "counted completions" for some things and that's the
    same code?

    Rather i suspect the real problem is not the name, but just not sure
    it gets abused. That is largely more a review problem and as far as I
    can figure out basically all the usual reviewers take care of that
    anyways. But renaming it also probably wouldn't hurt.

    [IMHO I always thought we should have a maintained single "list of
    things for reviewers to watch out for" list somewhere]

    -Andi



    \
     
     \ /
      Last update: 2008-04-15 19:17    [W:0.024 / U:0.064 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site