linux-kernel - Re: sem_lock() vs qspinlocks

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Message-ID: <CA+55aFyHVYh8VP9r1kohMomw=ed7y_=uQHDxtMsDCEcHKm+tFQ@mail.gmail.com>
Date:	Mon, 23 May 2016 10:52:09 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Boqun Feng <boqun.feng@...il.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Manfred Spraul <manfred@...orfullife.com>,
	Waiman Long <Waiman.Long@....com>,
	Ingo Molnar <mingo@...nel.org>, ggherdovich@...e.com,
	Mel Gorman <mgorman@...hsingularity.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Will Deacon <will.deacon@....com>
Subject: Re: sem_lock() vs qspinlocks

On Mon, May 23, 2016 at 5:25 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> Paul has smp_mb__after_unlock_lock() for the RCpc 'upgrade'. How about
> something like:
>
>         smp_mb__after_lock()

I'd much rather make the naming be higher level. It's not necessarily
going to be a "mb", and while the problem is about smp, the primitives
it is synchronizing aren't actually smp-specific (ie you're
synchronizing a lock that is relevant on UP too).

So I'd just call it something like

        spin_lock_sync_after_lock();

because different locks might have different levels of serialization
(ie maybe a spinlock needs one thing, and a mutex needs another - if
we start worrying about ordering between spin_lock and
mutex_is_locked(), for example, or between mutex_lock() and
spin_is_locked()).

Hmm?

                     Linus