From: David Laight <David.Laight@ACULAB.COM>
To: 'Yunfeng Ye' <yeyunfeng@huawei.com>,
"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
"will@kernel.org" <will@kernel.org>
Cc: "kstewart@linuxfoundation.org" <kstewart@linuxfoundation.org>,
"ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>,
"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"wuyun.wu@huawei.com" <wuyun.wu@huawei.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: RE: [PATCH] arm64: psci: Use udelay() instead of msleep() to reduce waiting time
Date: Thu, 12 Sep 2019 08:48:42 +0000 [thread overview]
Message-ID: <18c9fd22d72d4ea1a11e800e8873dd8d@AcuMS.aculab.com> (raw)
In-Reply-To: <e4d42bda-72f2-4002-f319-1cbe2bff74d2@huawei.com>
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
-
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next prev parent reply other threads:[~2019-09-12 8:48 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
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 [this message]
2019-09-16 15:26 ` Yunfeng Ye
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