Subject: Re: [PATCH V3] arm64: psci: Reduce waiting time for cpu_psci_cpu_kill()

From: Sudeep Holla <[email-masked]>
Date: Fri, 18 Oct 2019 12:45:29 +0100

On Fri, Oct 18, 2019 at 07:24:14PM +0800, Yunfeng Ye wrote:
> In a case like suspend-to-disk, a large number of CPU cores need to be

Add suspend-to-ram also to list, i.e.
"In case like suspend-to-disk and suspend-to-ram, a large number..."

> shut down. At present, the CPU hotplug operation is serialised, and the
> CPU cores can only be shut down one by one. In this process, if PSCI
> affinity_info() does not return LEVEL_OFF quickly, cpu_psci_cpu_kill()
> needs to wait for 10ms. If hundreds of CPU cores need to be shut down,
> it will take a long time.
>
> Normally, it is no need to wait 10ms in cpu_psci_cpu_kill(). So change

s/it is/there is/

> the wait interval from 10 ms to max 1 ms and use usleep_range() instead
> of msleep() for more accurate schedule.
>

s/for more accurate schedule/for more accurate timer/

> In addition, reduce the time interval will increase the messages output,

s/reduce/reducing/

> so remove the "Retry ..." message, instead, put the number of waiting
> times to the sucessful message.
> 
> Signed-off-by: Yunfeng Ye <[email-masked]>
> ---
> v2 -> v3:
>  - update the comment
>  - remove the busy-wait logic, modify the loop logic and output message
> 
> v1 -> v2:
>  - use usleep_range() instead of udelay() after waiting for a while
> 
>  arch/arm64/kernel/psci.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
> index c9f72b2665f1..00b8c0825a08 100644
> --- a/arch/arm64/kernel/psci.c
> +++ b/arch/arm64/kernel/psci.c
> @@ -91,15 +91,14 @@ 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++) {
> +	for (i = 0; i < 100; i++) {
>  		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);
> +			pr_info("CPU%d killed by waiting %d loops.\n", cpu, i);
>  			return 0;
>  		}
> 
> -		msleep(10);
> -		pr_info("Retrying again to check for CPU kill\n");
> +		usleep_range(100, 1000);

Since usleep_range can return anytime between 100us to 1ms, does it make
sense to check for (time_before(jiffies, timeout)) you had in v2 ?

--
Regards,
Sudeep

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