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

Sudeep Holla
2019-10-16T15:32:32Z

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 ?

> - }
> + /* 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 ?

We need more generic solution.

--
Regards,
Sudeep