linux-kernel - Re: [PATCH 2/3] cpumask: Introduce DYING mask

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Message-ID: <20210321193037.7o3mqcmwjthbos7n@e107158-lin>
Date:   Sun, 21 Mar 2021 19:30:37 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     valentin.schneider@....com, tglx@...utronix.de, mingo@...nel.org,
        bigeasy@...utronix.de, swood@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vincent.donnefort@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] cpumask: Introduce DYING mask

On 03/10/21 15:53, Peter Zijlstra wrote:
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -160,6 +160,9 @@ static int cpuhp_invoke_callback(unsigne
>  	int (*cb)(unsigned int cpu);
>  	int ret, cnt;
>  
> +	if (bringup != !cpu_dying(cpu))

nit: this condition is hard to read

> +		set_cpu_dying(cpu, !bringup);

since cpu_dying() will do cpumask_test_cpu(), are we saving  much if we
unconditionally call set_cpu_dying(cpu, !bringup) which performs
cpumask_{set, clear}_cpu()?

> +
>  	if (st->fail == state) {
>  		st->fail = CPUHP_INVALID;
>  		return -EAGAIN;

Thanks

--
Qais yousef