linux-kernel - Re: [PATCH v8 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock

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Date:   Tue, 21 Jan 2020 15:42:29 +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
Subject: Re: [PATCH v8 3/5] locking/qspinlock: Introduce CNA into the slow
 path of qspinlock

On Mon, Dec 30, 2019 at 02:40:40PM -0500, Alex Kogan wrote:
> +#define pv_wait_head_or_lock		cna_pre_scan

Also inconsitent naming.

> +__always_inline u32 cna_pre_scan(struct qspinlock *lock,
> +				  struct mcs_spinlock *node)
> +{
> +	struct cna_node *cn = (struct cna_node *)node;
> +
> +	cn->pre_scan_result = cna_scan_main_queue(node, node);
> +
> +	return 0;
> +}

The thinking here is that we're trying to make use of the time otherwise
spend spinning on atomic_cond_read_acquire(), to search for a potential
unlock candidate?

Surely that deserves a comment.