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

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Message-ID: <CA+55aFyR7Rt0-guH4TrrS83VQLsj-wrvQgOwvrf0UscRCxM-OA@mail.gmail.com>
Date:	Sat, 14 Apr 2012 09:58:07 -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 9:19 AM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
>
> This series is version two of the inlinable versions of preemptible
> RCU's __rcu_read_lock() and __rcu_read_unlock().  The first version may
> be found at https://lkml.org/lkml/2012/3/25/94.  The individual commits
> in this new series are as follows:

Ok, I'm looking at code generation changes for this now, and sadly (or
not) all the changes to the selinux code have actually  made the RCU
overhead that made me notice this issue originally much less
noticeable because we inline the right things etc, and that helped
with some of the problems that the rcu callsites had.

The fact that we don't have to indirect through "current" does seem to
make the code much simpler, though. So hopefully the actual rcu
unlocking code itself is better. But that was just under 1% of the
benchmark cost, so I was hoping that the call sites would be more
noticeable.

I'll see if it boots and what it does to my profiles and
microbenchmark, though.

                    Linus
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