linux-kernel - [PATCH] arm64: psci: Use udelay() instead of msleep() to reduce waiting time

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Date:   Wed, 11 Sep 2019 16:50:08 +0800
From:   Yunfeng Ye <yeyunfeng@...wei.com>
To:     <catalin.marinas@....com>, <will@...nel.org>
CC:     <kstewart@...uxfoundation.org>, <gregkh@...uxfoundation.org>,
        <ard.biesheuvel@...aro.org>, <tglx@...utronix.de>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <wuyun.wu@...wei.com>
Subject: [PATCH] arm64: psci: Use udelay() instead of msleep() to reduce
 waiting time

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@...wei.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