linux-kernel - Re: [PATCH v7 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock

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Message-ID: <20200122092238.GV14879@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Jan 2020 10:22:38 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alex Kogan <alex.kogan@...cle.com>
Cc:     linux@...linux.org.uk, mingo@...hat.com, will.deacon@....com,
        arnd@...db.de, longman@...hat.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, bp@...en8.de, hpa@...or.com, x86@...nel.org,
        guohanjun@...wei.com, jglauber@...vell.com,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        dave.dice@...cle.com, rahul.x.yadav@...cle.com
Subject: Re: [PATCH v7 3/5] locking/qspinlock: Introduce CNA into the slow
 path of qspinlock

On Tue, Jan 21, 2020 at 09:29:19PM +0100, Peter Zijlstra wrote:
> @@ -92,8 +92,8 @@ static int __init cna_init_nodes(void)
>  }
>  early_initcall(cna_init_nodes);
>  
> -static inline bool cna_try_change_tail(struct qspinlock *lock, u32 val,
> -				       struct mcs_spinlock *node)
> +static inline bool cna_try_clear_tail(struct qspinlock *lock, u32 val,
> +				      struct mcs_spinlock *node)
>  {
>  	struct mcs_spinlock *head_2nd, *tail_2nd;
>  	u32 new;

Also, that whole function is placed wrong; it should be between
cna_wait_head_or_lock() and cna_pass_lock(), then it's in the order they
appear in the slow path, ie. the order they actually run.