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    SubjectRe: [RFC][PATCH 0/5] Signal scalability series
    On Fri, 2011-09-30 at 16:56 -0700, Tejun Heo wrote:
    > Hello,
    > On Fri, Sep 30, 2011 at 09:00:23PM +0100, Matt Fleming wrote:
    > > On Fri, 2011-09-30 at 18:52 +0200, Oleg Nesterov wrote:
    > > Well, sighand->siglock is seriously overused. It protects so much and I
    > > think it's pretty confusing. It took me long enough to figure out how
    > > many locks were really needed. But that's beside the point, having a
    > > single lock doesn't scale at all, and that's what this series is about.
    > But scalability for what? What are the use cases here? Do we care
    > enough about benefits to those use cases to accept the increased
    > complexity? Having locks with broad coverage isn't necessarily evil.
    > If things are simpler that way and the protected paths aren't that
    > hot, who cares? If splitting the locking makes things simpler, sure
    > but that doesn't look like the case here, so we need pretty strong
    > rationale to justify the added complexity.

    I've Cc'd some -rt folks who have mentioned this bottleneck in the past.

    This patch series improves signal delivery scalability. Signals are
    still used heavily in legacy rt applications (as I'm hoping the -rt
    folks will attest to) and because everything is currently serialiesd
    with the per-process siglock, any heavy usage quickly hits that
    bottleneck. It's essentially a big-lock for signal delivery within a

    I also think Thomas/Peter mentioned something about latency in
    delivering timer signals because of contention on the per-process
    siglock. They might have some more details on that.

    Matt Fleming, Intel Open Source Technology Center

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