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From:   John Ogness <john.ogness@linutronix.de>
To:     paulmck@kernel.org
Cc:     rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com, rostedt@goodmis.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Petr Mladek <pmladek@suse.com>
Subject: Re: [PATCH RFC v2 rcu 1/8] srcu: Convert ->srcu_lock_count and
 ->srcu_unlock_count to atomic
In-Reply-To: <20220930153506.GD4196@paulmck-ThinkPad-P17-Gen-1>
References: <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1>
 <20220929180731.2875722-1-paulmck@kernel.org>
 <87ill4vrb9.fsf@jogness.linutronix.de>
 <20220930153506.GD4196@paulmck-ThinkPad-P17-Gen-1>
Date:   Fri, 30 Sep 2022 22:43:43 +0206
Message-ID: <87wn9k7g4o.fsf@jogness.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
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On 2022-09-30, "Paul E. McKenney" <paulmck@kernel.org> wrote:
>> > -	this_cpu_inc(ssp->sda->srcu_lock_count[idx]);
>> > +	this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter);
>> 
>> Is there any particular reason that you are directly modifying
>> @counter instead of raw_cpu_ptr()+atomic_long_inc() that do you in
>> __srcu_read_lock_nmisafe() of patch 2?
>
> Performance.  From what I can see, this_cpu_inc() is way faster than
> atomic_long_inc() on x86 and s390.  Maybe also on loongarch.  No idea
> on arm64.

Yeah, that's what I figured. I just wanted to make sure.

FWIW, the rest of the series looks pretty straight forward to me.

John