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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 2125DC49ED7 for ; Mon, 16 Sep 2019 15:26:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F091D2067B for ; Mon, 16 Sep 2019 15:26:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389117AbfIPP0i (ORCPT ); Mon, 16 Sep 2019 11:26:38 -0400 Received: from szxga07-in.huawei.com ([45.249.212.35]:51998 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726389AbfIPP0h (ORCPT ); Mon, 16 Sep 2019 11:26:37 -0400 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id A8D59719CC43F681D61C; Mon, 16 Sep 2019 23:26:32 +0800 (CST) Received: from [127.0.0.1] (10.177.251.225) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.439.0; Mon, 16 Sep 2019 23:26:25 +0800 Subject: Re: [PATCH] arm64: psci: Use udelay() instead of msleep() to reduce waiting time To: David Laight , "catalin.marinas@arm.com" , "will@kernel.org" CC: "kstewart@linuxfoundation.org" , "gregkh@linuxfoundation.org" , "ard.biesheuvel@linaro.org" , "tglx@linutronix.de" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "wuyun.wu@huawei.com" References: <18c9fd22d72d4ea1a11e800e8873dd8d@AcuMS.aculab.com> From: Yunfeng Ye Message-ID: Date: Mon, 16 Sep 2019 23:26:20 +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: <18c9fd22d72d4ea1a11e800e8873dd8d@AcuMS.aculab.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit 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 2019/9/12 16:48, David Laight wrote: > 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 >> --- >> 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 > Thanks for your advice. the delay depend on the num of cores, range from 50us to 500us, I have test the time on the 140+ cores cpu： (10us every time) [ 1177.979642] psci: CPU1 killed. total wait 4 times [ 1178.011369] psci: CPU2 killed. total wait 6 times [ 1178.035247] psci: CPU3 killed. total wait 3 times [ 1178.071134] psci: CPU4 killed. total wait 8 times ...... [ 1190.128202] psci: CPU139 killed. total wait 50 times [ 1190.156266] psci: CPU140 killed. total wait 48 times [ 1190.192082] psci: CPU141 killed. total wait 46 times [ 1190.224104] psci: CPU142 killed. total wait 46 times Can I bust-wait 1ms，which is 100 tiems udelay(10), after that, use usleep_range(1000, 10000) ? I don't want other process occupy cpu for a long time when I let out the cpu. thanks. > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >