linux-kernel - Re: [PATCH v8 5/5] locking/qspinlock: Introduce the shuffle reduction optimization into CNA

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Message-ID: <20200122095622.GS14914@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Jan 2020 10:56:22 +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 5/5] locking/qspinlock: Introduce the shuffle
 reduction optimization into CNA

On Mon, Dec 30, 2019 at 02:40:42PM -0500, Alex Kogan wrote:
> @@ -251,8 +281,11 @@ __always_inline u32 cna_pre_scan(struct qspinlock *lock,
>  	struct cna_node *cn = (struct cna_node *)node;
>  
>  	cn->pre_scan_result =
> -		cn->intra_count == intra_node_handoff_threshold ?
> -			FLUSH_SECONDARY_QUEUE : cna_scan_main_queue(node, node);
> +		(node->locked <= 1 && probably(SHUFFLE_REDUCTION_PROB_ARG)) ?
> +			PASS_LOCK_IMMEDIATELY :
> +			cn->intra_count == intra_node_handoff_threshold ?
> +				FLUSH_SECONDARY_QUEUE :
> +				cna_scan_main_queue(node, node);
>  
>  	return 0;
>  }

Let me just, once again, remind people that the Linux Kernel is not part
of the Obfuscated C code contest.

> Reviewed-by: Steve Sistare <steven.sistare@...cle.com>

Seriously, in what universe is that actually readable code? Steve quick,
say what it does.