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=-2.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 D7C92FA3728 for ; Wed, 16 Oct 2019 11:30:29 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 97FF821925 for ; Wed, 16 Oct 2019 11:30:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="epgTYlM9" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 97FF821925 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:To:Subject:Reply-To:Content-ID:Content-Description :Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=L3LBXMocJwqRq2R27Wjl3enqGZRPojEWfXXWIIzyfec=; b=epgTYlM9DQlt8+ OMWwWDPsUz/K7v/1AGM+uwXZ5vaulxg6EeV1PCXLkhNpDnh/bbW1kkcP02jv383FGCT5r27UMOIlE 5B3vr5xyxVAPmKSWSUhvpGmVNIm/wIj7P39LeCFI+lhbUAGwdww7txPXK/7UjN/EG1gfKUdHwxEw0 xqcLhU/PrXE7zNQda7ASKXWjp0SxqG+LzXSw1Tyv44wG+SfSWCW9GfkQwgUPvL0t6UBgdtEjLrQYw 55WNen4NyK8B5BHD8qEPpeEbFD8uq06PTfesf0CIGG6Mlz5JoOnmDszM6iwpokX53tnIofZe67upW 2DmZmqMXLXfo+gF2gdcQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1iKhVV-0007OW-1C; Wed, 16 Oct 2019 11:30:21 +0000 Received: from szxga06-in.huawei.com ([45.249.212.32] helo=huawei.com) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1iKhVR-0007Fm-ME for linux-arm-kernel@lists.infradead.org; Wed, 16 Oct 2019 11:30:19 +0000 Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id E10A368E0175608A4F90; Wed, 16 Oct 2019 19:30:15 +0800 (CST) Received: from [127.0.0.1] (10.177.251.225) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.439.0; Wed, 16 Oct 2019 19:30:07 +0800 Subject: Re: [PATCH V2] arm64: psci: Reduce waiting time of cpu_psci_cpu_kill() To: Sudeep Holla References: <18068756-0f39-6388-3290-cf03746e767d@huawei.com> <20191015162358.bt5rffidkv2j4xqb@willie-the-truck> <20191016102545.GA11386@bogus> From: Yunfeng Ye Message-ID: <13d82e24-90bd-0c17-ef7f-aa7fec272f59@huawei.com> Date: Wed, 16 Oct 2019 19:29:59 +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: <20191016102545.GA11386@bogus> Content-Language: en-US X-Originating-IP: [10.177.251.225] X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191016_043017_880329_BC195C5F X-CRM114-Status: GOOD ( 22.78 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "kstewart@linuxfoundation.org" , "ard.biesheuvel@linaro.org" , hushiyuan@huawei.com, "catalin.marinas@arm.com" , "linux-kernel@vger.kernel.org" , linfeilong@huawei.com, David Laight , "gregkh@linuxfoundation.org" , "tglx@linutronix.de" , "wuyun.wu@huawei.com" , Will Deacon , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2019/10/16 18:25, Sudeep Holla wrote: > On Wed, Oct 16, 2019 at 11:22:23AM +0800, Yunfeng Ye wrote: >> >> >> On 2019/10/16 0:23, Will Deacon wrote: >>> Hi, >>> >>> On Sat, Sep 21, 2019 at 07:21:17PM +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. >>> >>> Can you elaborate on "the right case" please? It's not clear to me >>> exactly what problem you're solving here. >>> >> The situation is that when the power is off, we have a battery to save some >> information, but the battery power is limited, so we reduce the power consumption >> by turning off the cores, and need fastly to complete the core shutdown. However, the >> time of cpu_psci_cpu_kill() will take 10ms. We have tested the time that it does not >> need 10ms, and most case is about 50us-500us. if we reduce the time of cpu_psci_cpu_kill(), >> we can reduce 10% - 30% of the total time. >> > > Have you checked why PSCI AFFINITY_INFO not returning LEVEL_OFF quickly > then ? We wait for upto 5s in cpu_wait_death(worst case) before cpu_kill > is called from __cpu_die. > When cpu_wait_death() is done, it means that the cpu core's hardware prepare to die. I think not returning LEVEL_OFF quickly is that hardware need time to handle. I don't know how much time it need is reasonable, but I test that it need about 50us - 500us. In addition I have not meat the worst case that cpu_wait_death() need upto 5s, and we only take normal case into account. thanks. > Moreover I don't understand the argument here. The cpu being killed > will be OFF, as soon as it can and firmware controls that and this > change is not related to CPU_OFF. And this CPU calling cpu_kill can > sleep and 10ms is good to enter idle states if it's idle saving power, > so I fail to map the power saving you mention above. > We have hundreds of CPU cores that need to be shut down. For example, a CPU has 200 cores, and the thread to shut down the core is in CPU 0. and the thread need to shut down from core 1 to core 200. However, the implementation of the kernel can only shut down cpu cores one by one, so we need to wait for cpu_kill() to finish before shutting down the next CPU core. If it wait for 10ms each time in cpu_kill, it will takes up about 2 seconds in cpu_kill() total. It is not to save power through msleep to idle state, but to quickly turn off other CPU core's hardware to reduce power consumption. thanks. >> So change msleep (10) to usleep_range() to reduce the waiting time. In addition, >> we don't want to be scheduled during the sleeping time, some threads may take a >> long time and don't give up the CPU, which affects the time of core shutdown, >> Therefore, we add a chance to busy-wait max 1ms. >> > > On the other hand, usleep_range reduces the timer interval and hence > increases the chance of the callee CPU not to enter deeper idle states. > > What am I missing here ? What's the use case or power off situation > you are talking about above ? > As mentioned above, we are not to save power through msleep to idle state, but to quickly turn off other CPU core's hardware to reduce power consumption. >> >>> I've also added Sudeep to the thread, since I'd like his ack on the change. >>> > > Thanks Will. > > -- > Regards, > Sudeep > > . > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel