linux-kernel - Re: [PATCH v4] arm64: psci: Reduce the waiting time for cpu_psci_cpu

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Date:   Mon, 21 Oct 2019 15:47:17 +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>, <mark.rutland@....com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <hushiyuan@...wei.com>,
        <wuyun.wu@...wei.com>, <linfeilong@...wei.com>
Subject: Re: [PATCH v4] arm64: psci: Reduce the waiting time for
 cpu_psci_cpu_kill()



On 2019/10/18 23:20, Sudeep Holla wrote:
> On Fri, Oct 18, 2019 at 08:46:37PM +0800, Yunfeng Ye wrote:
>> In case like suspend-to-disk and uspend-to-ram, a large number of CPU
> 
> s/case/cases/
> s/uspend-to-ram/suspend-to-ram/
> 
ok, thanks.

>> cores need to be 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, there is no need to wait 10ms in cpu_psci_cpu_kill(). So
>> change the wait interval from 10 ms to max 1 ms and use usleep_range()
>> instead of msleep() for more accurate timer.
>>
>> In addition, reducing the time interval will increase the messages
>> output, so remove the "Retry ..." message, instead, put the number of
>> waiting times to the sucessful message.
>>
>> Signed-off-by: Yunfeng Ye <yeyunfeng@...wei.com>
>> ---
>> v3 -> v4:
>>  - using time_before(jiffies, timeout) to check
>>  - update the comment as review suggest
>>
>> 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 | 14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
>> index c9f72b2665f1..77965c3ba477 100644
>> --- a/arch/arm64/kernel/psci.c
>> +++ b/arch/arm64/kernel/psci.c
>> @@ -81,7 +81,8 @@ static void cpu_psci_cpu_die(unsigned int cpu)
>>
>>  static int cpu_psci_cpu_kill(unsigned int cpu)
>>  {
>> -	int err, i;
>> +	int err, i = 0;
>> +	unsigned long timeout;
>>
>>  	if (!psci_ops.affinity_info)
>>  		return 0;
>> @@ -91,16 +92,17 @@ 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++) {
>> +	timeout = jiffies + msecs_to_jiffies(100);
>> +	do {
>> +		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 (polled %d times)\n", cpu, i);
> 
> We can even drop loop counter completely, track time and log that
> instead of loop counter that doesn't give any indication without looking
> into the code.
> 
ok, I will modify as your suggest. thanks.

> 	start = jiffies, end = start + msecs_to_jiffies(100);
> 	do {
> 			....
> 			pr_info("CPU%d killed (polled %u ms)\n", cpu,
> 				jiffies_to_msecs(jiffies - start));
> 			....
> 	} while (time_before(jiffies, end));
> 
> Just my preference. Looks good otherwise.
> 
> --
> Regards,
> Sudeep
> 
> 
> .
>