linux-kernel - Re: [PATCH v14 4/6] locking/qspinlock: Introduce starvation avoidance into CNA

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Message-ID: <87mtu2vhzz.fsf@linux.intel.com>
Date:   Mon, 12 Apr 2021 23:03:12 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Alex Kogan <alex.kogan@...cle.com>
Cc:     linux@...linux.org.uk, peterz@...radead.org, 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 v14 4/6] locking/qspinlock: Introduce starvation avoidance into CNA

Alex Kogan <alex.kogan@...cle.com> writes:
>  
> +	numa_spinlock_threshold=	[NUMA, PV_OPS]
> +			Set the time threshold in milliseconds for the
> +			number of intra-node lock hand-offs before the
> +			NUMA-aware spinlock is forced to be passed to
> +			a thread on another NUMA node.	Valid values
> +			are in the [1..100] range. Smaller values result
> +			in a more fair, but less performant spinlock,
> +			and vice versa. The default value is 10.

ms granularity seems very coarse grained for this. Surely
at some point of spinning you can afford a ktime_get? But ok.

Could you turn that into a moduleparm which can be changed at runtime?
Would be strange to have to reboot just to play with this parameter

This would also make the code a lot shorter I guess.

-Andi