From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DAC21ECE58E for ; Thu, 17 Oct 2019 14:25:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B86C42089C for ; Thu, 17 Oct 2019 14:25:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2395218AbfJQOZD (ORCPT ); Thu, 17 Oct 2019 10:25:03 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:4217 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727671AbfJQOZD (ORCPT ); Thu, 17 Oct 2019 10:25:03 -0400 Received: from DGGEMS404-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id A4744BDAD13C9CDF3576; Thu, 17 Oct 2019 22:24:59 +0800 (CST) Received: from [127.0.0.1] (10.177.251.225) by DGGEMS404-HUB.china.huawei.com (10.3.19.204) with Microsoft SMTP Server id 14.3.439.0; Thu, 17 Oct 2019 22:24:51 +0800 Subject: Re: [PATCH V2] arm64: psci: Reduce waiting time of cpu_psci_cpu_kill() To: Sudeep Holla CC: David Laight , "catalin.marinas@arm.com" , "will@kernel.org" , "kstewart@linuxfoundation.org" , "gregkh@linuxfoundation.org" , "ard.biesheuvel@linaro.org" , "tglx@linutronix.de" , "wuyun.wu@huawei.com" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , , References: <18068756-0f39-6388-3290-cf03746e767d@huawei.com> <9df267db-e647-a81d-16bb-b8bfb06c2624@huawei.com> <20191016153221.GA8978@bogus> <0f550044-9ed2-5f72-1335-73417678ba45@huawei.com> <20191017135416.GA26312@bogus> From: Yunfeng Ye Message-ID: <0b3b8684-e840-ba32-6e42-d23fcadf7e65@huawei.com> Date: Thu, 17 Oct 2019 22:24:33 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20191017135416.GA26312@bogus> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.251.225] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/10/17 21:54, Sudeep Holla wrote: > On Thu, Oct 17, 2019 at 09:26:15PM +0800, Yunfeng Ye wrote: >> >> >> On 2019/10/16 23:32, Sudeep Holla wrote: >>> 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 >>>> --- >>>> 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 ? >>> >> When reduce the time interval to 1ms, the print message maybe increase 10 >> times. on the other hand, cpu_psci_cpu_kill() will print message on success >> or failure, which this retry log is not very necessary. of cource, I think >> use pr_info_once() instead of pr_info() is better. >> > > Yes changing it to pr_info_once is better than dropping it as it gives > some indication to the firmware if there's scope for improvement. > >>>> - } >>>> + /* 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 ? >>> >> msleep() is implemented by jiffies. when HZ=100 or HZ=250, msleep(1) is not >> accurate. so I think usleep_range() is better. 1 ms looks simple and good, but how >> about 100us is better? I refer a function sunxi_mc_smp_cpu_kill(), it use >> usleep_range(50, 100). >> > > Again that's specific to sunxi platforms and may work well. While I agree > msleep(1) may not be accurate, I am still inclined to have a max value > of 1000(i.e. 1ms) for usleep_range. > ok, I will send a new version patch that waiting max 1ms. thanks. > -- > Regards, > Sudeep > > . >