Re: [PATCH V2] arm64: psci: Reduce waiting time of cpu_psci_cpu_kill()

Yunfeng Ye
2019-10-17T13:26:32Z

On 2019/10/16 23:32, Sudeep Holla wrote:
> On Wed, Oct 09, 2019 at 12:45:16PM +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.
>>
>> Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
>> ---
>> V1->V2:
>> - use usleep_range() instead of udelay() after waiting for a while
>>
>> 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");
>
> You dropped this message, any particular reason ?
>
When reduce the time interval to 1ms, the print message maybe increase 10 times.
on the other hand, cpu_psci_cpu_kill() will print message on success or failure, which
this retry log is not very necessary. of cource, I think use pr_info_once() instead of
pr_info() is better.

thanks.

>> - }
>> + /* busy-wait max 1ms */
>> + if (i++ < 100) {
>> + cond_resched();
>> + udelay(10);
>> + continue;
>
> Why can't it be simple like loop of 100 * msleep(1) instead of loop of
> 10 * msleep(10). The above initial busy wait for 1 ms looks too much
> optimised for your setup where it takes 50-500us, what if it take just
> over 1 ms ?
>
msleep() is implemented by jiffies. when HZ=100 or HZ=250, msleep(1) is not
accurate. so I think usleep_range() is better. 1 ms looks simple and good, but how
about 100us is better? I refer a function sunxi_mc_smp_cpu_kill(), it use
usleep_range(50, 100).

thanks.

> We need more generic solution.
>
> --
> Regards,
> Sudeep
>
> .
>