[PATCH V3] arm64: psci: Reduce waiting time for cpu_psci_cpu_kill()

[Yunfeng Ye]

In a case like suspend-to-disk, a large number of CPU 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, it 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 schedule.

In addition, reduce 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@xxxxxxxxxx>
---
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);
 	}

 	pr_warn("CPU%d may not have shut down cleanly (AFFINITY_INFO reports %d)\n",
-- 
2.7.4.3