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

[Paul E. McKenney]

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/