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

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Date:   Fri, 18 Oct 2019 20:46:37 +0800
From:   Yunfeng Ye <yeyunfeng@...wei.com>
To:     <catalin.marinas@....com>, <will@...nel.org>,
        <kstewart@...uxfoundation.org>, <sudeep.holla@....com>,
        <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: [PATCH v4] arm64: psci: Reduce the waiting time for
 cpu_psci_cpu_kill()

In case like suspend-to-disk and uspend-to-ram, 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, 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);
 			return 0;
 		}

-		msleep(10);
-		pr_info("Retrying again to check for CPU kill\n");
-	}
+		usleep_range(100, 1000);
+	} while (time_before(jiffies, timeout));

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