linux-kernel - Re: [PATCH V2] arm64: psci: Reduce waiting time of cpu_psci_cpu

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Date:   Tue, 15 Oct 2019 17:23:59 +0100
From:   Will Deacon <will@...nel.org>
To:     Yunfeng Ye <yeyunfeng@...wei.com>, sudeep.holla@....com
Cc:     David Laight <David.Laight@...LAB.COM>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "kstewart@...uxfoundation.org" <kstewart@...uxfoundation.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "wuyun.wu@...wei.com" <wuyun.wu@...wei.com>
Subject: Re: [PATCH V2] arm64: psci: Reduce waiting time of
 cpu_psci_cpu_kill()

Hi,

On Sat, Sep 21, 2019 at 07:21:17PM +0800, Yunfeng Ye wrote:
> If psci_ops.affinity_info() fails, it will sleep 10ms, which will not
> take so long in the right case. Use usleep_range() instead of msleep(),
> reduce the waiting time, and give a chance to busy wait before sleep.

Can you elaborate on "the right case" please? It's not clear to me
exactly what problem you're solving here.

I've also added Sudeep to the thread, since I'd like his ack on the change.

Will

>  arch/arm64/kernel/psci.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
> index c9f72b2..99b3122 100644
> --- a/arch/arm64/kernel/psci.c
> +++ b/arch/arm64/kernel/psci.c
> @@ -82,6 +82,7 @@ static void cpu_psci_cpu_die(unsigned int cpu)
>  static int cpu_psci_cpu_kill(unsigned int cpu)
>  {
>  	int err, i;
> +	unsigned long timeout;
> 
>  	if (!psci_ops.affinity_info)
>  		return 0;
> @@ -91,16 +92,24 @@ static int cpu_psci_cpu_kill(unsigned int cpu)
>  	 * while it is dying. So, try again a few times.
>  	 */
> 
> -	for (i = 0; i < 10; i++) {
> +	i = 0;
> +	timeout = jiffies + msecs_to_jiffies(100);
> +	do {
>  		err = psci_ops.affinity_info(cpu_logical_map(cpu), 0);
>  		if (err == PSCI_0_2_AFFINITY_LEVEL_OFF) {
>  			pr_info("CPU%d killed.\n", cpu);
>  			return 0;
>  		}
> 
> -		msleep(10);
> -		pr_info("Retrying again to check for CPU kill\n");
> -	}
> +		/* busy-wait max 1ms */
> +		if (i++ < 100) {
> +			cond_resched();
> +			udelay(10);
> +			continue;
> +		}
> +
> +		usleep_range(100, 1000);
> +	} while (time_before(jiffies, timeout));
> 
>  	pr_warn("CPU%d may not have shut down cleanly (AFFINITY_INFO reports %d)\n",
>  			cpu, err);
> -- 
> 2.7.4.huawei.3
>