[lkml]   [2011]   [Oct]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [RFC][PATCH 0/5] Signal scalability series
    On Mon, 2011-10-03 at 15:07 +0200, Oleg Nesterov wrote:
    > On 10/01, Peter Zijlstra wrote:

    > But this series can't help afaics. At least in its current state. It
    > only adds more locking to the sending paths.

    Right, so I was hoping Matt had a plan (TM)... :-)

    > And anyway it is wrong (afaics, and I didn't read it yet ;).

    I'll leave you to be the judge of that, I haven't bent by brain around
    all this signal stuff yet..

    > > which precludes being able
    > > to deliver signals from hardirq context, leading to lots of ugly in -rt.
    > I think, the best solution would be: never send the signal from irq
    > context, and ->siglock shouldn't disable irqs.

    Bit hard that, posix timers need to deliver signals which pretty much
    mandates we do something from irq context (and the round-trip through
    softirq context really isn't pretty nor good for performance).

    > > The hope is that this work is a stepping stone to O(1) signal delivery.
    > Probably this is possible too. I was thinking anout this when
    > set_current_blocked() was added. Unfortunately this needs a lot of
    > complications.

    Right, so the thing Thomas and I have been promoting for a while now is
    to update a signal target vector on every signal mask update. Mask
    updates should be the slow path. This would leave us with a ready target
    in O(1).

    Although given that we've promoted this idea for a while now and it
    hasn't happened yet I'm sure its non-trivial :-)

    > > Breaking up the multitude of uses of siglock certainly seems worthwhile
    > > esp.
    > Agreed. But I am not sure how much we should split the locking when
    > it comes to sending/dequeueing/etc signals. 5 locks seems too much.

    It doesn't need all 5 locks to send a signal, does it? But then, I'm
    somewhat out of my depth here, the whole signal delivery path always
    looses me.

    > > And yes, aside from that the siglock can be quite contended because its
    > > pretty much the one lock serializing all of the process wide state.
    > True.
    > Mostly this is because we moved misc stuff from tasklist to siglock,
    > previously this was a win. Today this doesn't look good.

    Well a per-process lock still wins from a global lock, but yeah, it
    wants to be broken up further.

     \ /
      Last update: 2011-10-03 17:25    [W:0.021 / U:0.024 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site