Re: [PATCH RFC 0/7] rcu: v2 Inlinable preemptible rcu_read_lock()and rcu_read_unlock()

[Paul E. McKenney]

On Sat, Apr 14, 2012 at 10:08:54AM -0700, Linus Torvalds wrote:
> On Sat, Apr 14, 2012 at 9:58 AM, Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > I'll see if it boots and what it does to my profiles and
> > microbenchmark, though.
> 
> Ok, I can't see any performance difference in the numbers - my
> benchmark noise is *much* bigger than anything this would show.

Might still be worthwhile on embedded CPUs that don't optimize
function calls as thoroughly as does x86, maybe?

> The profile looks fine, and obviously __rcu_read_lock() is entirely
> gone. The top user (avc_has_perm_flags()) looks fine. I note that you
> might want to look at the placement of the percpu data - I think it
> probably makes sense to put the RCU data close to 'current' etc to get
> as much cacheline sharing as possible, and it doesn't seem to be right
> now, but it looks reasonable.

Is there somewhere in non-architecture-specific code that would be a
good place to put this?  Or is the DEFINE_PER_CPU() for current_task
moving from arch/x86 to core code?

> But on the whole, I can't claim that it looks noticeable ;*(

Well, then, I guess I don't feel quite so bad about having prioritized
this so low for so long.  ;-)

							Thanx, Paul

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