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    SubjectRe: workqueue thing

    * Tejun Heo <tj@kernel.org> wrote:

    > Hello, Ingo.
    >
    > On 12/23/2009 05:12 PM, Ingo Molnar wrote:
    > >
    > > * Ingo Molnar <mingo@elte.hu> wrote:
    > >
    > >> At least as far as i'm concerned, i'd like to see actual uses. It's a big
    > >> linecount increase all things considered:
    > >>
    > >> 20 files changed, 2783 insertions(+), 660 deletions(-)
    >
    > BTW, the code contains way more comment afterwards and has other benefits
    > like not having crazy number of workers around on many core machines.

    (the original workqueue.c had way more comments as well.)

    > >> and you say it _wont_ help performance/scalability (this aspect wasnt clear
    >
    > And I think it will help scalability for sure although it depends on
    > what type of scalability you're talking about.

    _I_ am not making any claims - i am simply asking what the benefits are, just
    to move the discussion forward. If there are benefits, it must be measurable,
    simple as that.

    > >> to me from previous discussions), so the (yet to be seen) complexity
    > >> reduction in other code ought to be worth it.
    > >
    > > To further stress this point, i'd like to point to the very first commit that
    > > introduced kernel/workqueue.c into Linux 7 years ago:
    > >
    > > | From 6ed12ff83c765aeda7d38d3bf9df7d46d24bfb11 Mon Sep 17 00:00:00 2001
    > > | From: Ingo Molnar <mingo@elte.hu>
    > > | Date: Mon, 30 Sep 2002 22:17:42 -0700
    > > | Subject: [PATCH] [PATCH] Workqueue Abstraction
    > >
    > > look at the diffstat of that commit:
    > >
    > > 201 files changed, 1102 insertions(+), 1194 deletions(-)
    > >
    > > despite adding a new abstraction and kernel subsystem (workqueues), that
    > > commit modified more than a hundred drivers to make use of it, and managed to
    > > achieve a net linecount decrease of 92 lines - despite adding hundreds of
    > > lines of a new core facility.
    > >
    > > Likewise, for this particular patchset it should be possible to identify
    > > existing patterns of code in the existing code base of 6+ millions lines of
    > > Linux driver code that would make the advantages of this +2000 lines of core
    > > kernel code plain obvious. There were multipe claims of problems with the
    > > current abstractions - so there sure must be a way to show off the new code in
    >
    > I'm not sure I'm gonna update that many places in a single sweep but yeah
    > let's give it a shot.

    In all fairness the original workqueue.c had an advantage, that it basically
    piggybacked on usable patterns from the tqueue (task-queue) abstraction - and
    that was rather repetitive.

    Your code adds a new _paradigm_ for which no easily reusable patterns exist -
    so under no way are you expected to show such a massive amount of conversion -
    just a handful of cases would be enough to show the benefits - we can
    extrapolate from there.

    It would also give us hands-on experience with the utility (and robustness) of
    your proposal, so it's a win-win proposal IMO.

    Thanks,

    Ingo


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