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SubjectRe: [PATCH] hotplug: Optimize {get,put}_online_cpus()
On Mon, Sep 23, 2013 at 06:01:30PM +0200, Peter Zijlstra wrote:
> On Mon, Sep 23, 2013 at 08:50:59AM -0700, Paul E. McKenney wrote:
> > Not a problem, just stuff the idx into some per-task thing. Either
> > task_struct or taskinfo will work fine.
>
> Still not seeing the point of using srcu though..
>
> srcu_read_lock() vs synchronize_srcu() is the same but far more
> expensive than preempt_disable() vs synchronize_sched().

Heh! You want the old-style SRCU. ;-)

> > Or to put it another way, if the underlying slow-path mutex is
> > reader-preference, then the whole thing will be reader-preference.
>
> Right, so 1) we have no such mutex so we're going to have to open-code
> that anyway, and 2) like I just explained in the other email, I want the
> pending writer case to be _fast_ as well.

At some point I suspect that we will want some form of fairness, but in
the meantime, good point.

Thanx, Paul



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