linux-kernel - Re: [PATCH RFC 0/7] rcu: v2 Inlinable preemptible rcu_read_lock() and rcu_read

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Message-ID: <CA+55aFzrmg2Fqg9VD9zV==gxiimW_By2zM17AvJXKY5ecX-ang@mail.gmail.com>
Date:	Sat, 14 Apr 2012 10:08:54 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...icios.com, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org
Subject: Re: [PATCH RFC 0/7] rcu: v2 Inlinable preemptible rcu_read_lock() and rcu_read_unlock()

On Sat, Apr 14, 2012 at 9:58 AM, Linus Torvalds
<torvalds@...ux-foundation.org> 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.

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.

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

                   Linus
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