linux-kernel - Re: [PATCH 1/8] locking: Introduce local

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Date:   Fri, 22 May 2020 13:05:56 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/8] locking: Introduce local_lock()

On 2020-05-20 14:04:50 [+0200], Peter Zijlstra wrote:
> On Tue, May 19, 2020 at 10:19:05PM +0200, Sebastian Andrzej Siewior wrote:
> > +/**
> > + * DEFINE_LOCAL_LOCK - Define and initialize a per CPU local lock
> > + * @lock:	Name of the lock instance
> > + */
> > +#define DEFINE_LOCAL_LOCK(lvar)					\
> > +	DEFINE_PER_CPU(struct local_lock, lvar) = { INIT_LOCAL_LOCK(lvar) }
> > +
> > +/**
> > + * DECLARE_LOCAL_LOCK - Declare a defined per CPU local lock
> > + * @lock:	Name of the lock instance
> > + */
> > +#define DECLARE_LOCAL_LOCK(lvar)				\
> > +	DECLARE_PER_CPU(struct local_lock, lvar)
> 
> So I think I'm going to argue having these is a mistake. The local_lock
> should be put in a percpu structure along with the data it actually
> protects.

So I got rid of these and made the local_lock part of the per-CPU
struct.

> > +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> > +# define LL_DEP_MAP_INIT(lockname)	.dep_map = { .name = #lockname }
> 
> That wants to be:
> 
> 	.dep_map = {
> 		.name = #lockname,
> 		.wait_type_inner = LD_WAIT_SPIN,

Why LD_WAIT_SPIN and not LD_WAIT_SLEEP? On RT the lock becomes sleeping
and none of the SPIN restrictions apply. 

> 	}
> 
> > +#else
> > +# define LL_DEP_MAP_INIT(lockname)
> > +#endif

Sebastian