linux-kernel - Re: [PATCH V3] arm64: psci: Reduce waiting time for cpu_psci_cpu

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Date:   Fri, 18 Oct 2019 20:03:28 +0800
From:   Yunfeng Ye <yeyunfeng@...wei.com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     <catalin.marinas@....com>, <will@...nel.org>,
        <kstewart@...uxfoundation.org>, <gregkh@...uxfoundation.org>,
        <lorenzo.pieralisi@....com>, <tglx@...utronix.de>,
        <David.Laight@...LAB.COM>, <ard.biesheuvel@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        "hushiyuan@...wei.com" <hushiyuan@...wei.com>,
        <wuyun.wu@...wei.com>,
        "linfeilong@...wei.com" <linfeilong@...wei.com>
Subject: Re: [PATCH V3] arm64: psci: Reduce waiting time for
 cpu_psci_cpu_kill()



On 2019/10/18 19:45, Sudeep Holla wrote:
> 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..."
> 
ok, thanks.

>> 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/
> 
ok, thanks.

>> 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/
> 
ok, thanks.

>> In addition, reduce the time interval will increase the messages output,
> 
> s/reduce/reducing/
> 
ok, thanks.

>> so remove the "Retry ..." message, instead, put the number of waiting
>> times to the sucessful message.
>>
>> Signed-off-by: Yunfeng Ye <yeyunfeng@...wei.com>
>> ---
>> 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 ?
> 
ok, if using (time_before(jiffies, timeout)), the output message change to print
waiting xxx jiffies ? or still print the number of loops?

> --
> Regards,
> Sudeep
> 
> .
>