* [PATCH] arm64: psci: Use udelay() instead of msleep() to reduce waiting time
@ 2019-09-11 8:50 Yunfeng Ye
2019-09-12 8:48 ` David Laight
0 siblings, 1 reply; 3+ messages in thread
From: Yunfeng Ye @ 2019-09-11 8:50 UTC (permalink / raw)
To: catalin.marinas, will
Cc: kstewart, ard.biesheuvel, gregkh, linux-kernel, tglx, wuyun.wu,
linux-arm-kernel
We want to reduce the time of cpu_down() for saving power, found that
cpu_psci_cpu_kill() cost 10ms after psci_ops.affinity_info() fail.
Normally the time cpu dead is very short, it is no need to wait 10ms.
so use udelay 10us to instead msleep 10ms in every waiting loop, and add
cond_resched() to give a chance to run a higher-priority process.
Signed-off-by: Yunfeng Ye <yeyunfeng@huawei•com>
---
arch/arm64/kernel/psci.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
index 85ee7d0..9e9d8a6 100644
--- a/arch/arm64/kernel/psci.c
+++ b/arch/arm64/kernel/psci.c
@@ -86,15 +86,15 @@ 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 < 10000; 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);
return 0;
}
- msleep(10);
- pr_info("Retrying again to check for CPU kill\n");
+ cond_resched();
+ udelay(10);
}
pr_warn("CPU%d may not have shut down cleanly (AFFINITY_INFO reports %d)\n",
--
1.8.3.1
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^ permalink raw reply related [flat|nested] 3+ messages in thread* RE: [PATCH] arm64: psci: Use udelay() instead of msleep() to reduce waiting time
2019-09-11 8:50 [PATCH] arm64: psci: Use udelay() instead of msleep() to reduce waiting time Yunfeng Ye
@ 2019-09-12 8:48 ` David Laight
2019-09-16 15:26 ` Yunfeng Ye
0 siblings, 1 reply; 3+ messages in thread
From: David Laight @ 2019-09-12 8:48 UTC (permalink / raw)
To: 'Yunfeng Ye', catalin.marinas@arm•com, will@kernel•org
Cc: kstewart@linuxfoundation•org, ard.biesheuvel@linaro•org,
gregkh@linuxfoundation•org, linux-kernel@vger•kernel.org,
tglx@linutronix•de, wuyun.wu@huawei•com,
linux-arm-kernel@lists•infradead.org
From: Yunfeng Ye
> Sent: 11 September 2019 09:50
> We want to reduce the time of cpu_down() for saving power, found that
> cpu_psci_cpu_kill() cost 10ms after psci_ops.affinity_info() fail.
>
> Normally the time cpu dead is very short, it is no need to wait 10ms.
> so use udelay 10us to instead msleep 10ms in every waiting loop, and add
> cond_resched() to give a chance to run a higher-priority process.
>
> Signed-off-by: Yunfeng Ye <yeyunfeng@huawei•com>
> ---
> arch/arm64/kernel/psci.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
> index 85ee7d0..9e9d8a6 100644
> --- a/arch/arm64/kernel/psci.c
> +++ b/arch/arm64/kernel/psci.c
> @@ -86,15 +86,15 @@ 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 < 10000; 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);
> return 0;
> }
>
> - msleep(10);
> - pr_info("Retrying again to check for CPU kill\n");
> + cond_resched();
> + udelay(10);
You really don't want to be doing 10000 udelay(10) before giving up.
If udelay(10) is long enough for the normal case, then do that once.
After that use usleep_range().
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] arm64: psci: Use udelay() instead of msleep() to reduce waiting time
2019-09-12 8:48 ` David Laight
@ 2019-09-16 15:26 ` Yunfeng Ye
0 siblings, 0 replies; 3+ messages in thread
From: Yunfeng Ye @ 2019-09-16 15:26 UTC (permalink / raw)
To: David Laight, catalin.marinas@arm•com, will@kernel•org
Cc: kstewart@linuxfoundation•org, ard.biesheuvel@linaro•org,
gregkh@linuxfoundation•org, linux-kernel@vger•kernel.org,
tglx@linutronix•de, wuyun.wu@huawei•com,
linux-arm-kernel@lists•infradead.org
On 2019/9/12 16:48, David Laight wrote:
> From: Yunfeng Ye
>> Sent: 11 September 2019 09:50
>> We want to reduce the time of cpu_down() for saving power, found that
>> cpu_psci_cpu_kill() cost 10ms after psci_ops.affinity_info() fail.
>>
>> Normally the time cpu dead is very short, it is no need to wait 10ms.
>> so use udelay 10us to instead msleep 10ms in every waiting loop, and add
>> cond_resched() to give a chance to run a higher-priority process.
>>
>> Signed-off-by: Yunfeng Ye <yeyunfeng@huawei•com>
>> ---
>> arch/arm64/kernel/psci.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
>> index 85ee7d0..9e9d8a6 100644
>> --- a/arch/arm64/kernel/psci.c
>> +++ b/arch/arm64/kernel/psci.c
>> @@ -86,15 +86,15 @@ 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 < 10000; 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);
>> return 0;
>> }
>>
>> - msleep(10);
>> - pr_info("Retrying again to check for CPU kill\n");
>> + cond_resched();
>> + udelay(10);
>
> You really don't want to be doing 10000 udelay(10) before giving up.
>
> If udelay(10) is long enough for the normal case, then do that once.
> After that use usleep_range().
> > David
>
Thanks for your advice. the delay depend on the num of cores, range
from 50us to 500us, I have test the time on the 140+ cores cpu：
(10us every time)
[ 1177.979642] psci: CPU1 killed. total wait 4 times
[ 1178.011369] psci: CPU2 killed. total wait 6 times
[ 1178.035247] psci: CPU3 killed. total wait 3 times
[ 1178.071134] psci: CPU4 killed. total wait 8 times
......
[ 1190.128202] psci: CPU139 killed. total wait 50 times
[ 1190.156266] psci: CPU140 killed. total wait 48 times
[ 1190.192082] psci: CPU141 killed. total wait 46 times
[ 1190.224104] psci: CPU142 killed. total wait 46 times
Can I bust-wait 1ms，which is 100 tiems udelay(10), after that, use
usleep_range(1000, 10000) ? I don't want other process occupy cpu
for a long time when I let out the cpu. thanks.
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-09-11 8:50 [PATCH] arm64: psci: Use udelay() instead of msleep() to reduce waiting time Yunfeng Ye
2019-09-12 8:48 ` David Laight
2019-09-16 15:26 ` Yunfeng Ye
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