Re: [PATCH] hotplug: Optimize {get,put}_online_cpus()

[Peter Zijlstra]

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().

> 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.
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