From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id D95B443D51; Tue, 26 Mar 2024 13:15:26 +0100 (CET) Received: from mails.dpdk.org (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id 90BFB40265; Tue, 26 Mar 2024 13:15:25 +0100 (CET) Received: from szxga05-in.huawei.com (szxga05-in.huawei.com [45.249.212.191]) by mails.dpdk.org (Postfix) with ESMTP id 659E540261 for ; Tue, 26 Mar 2024 13:15:23 +0100 (CET) Received: from mail.maildlp.com (unknown [172.19.162.112]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4V3pbD4N3Rz1h3yF; Tue, 26 Mar 2024 20:12:40 +0800 (CST) Received: from kwepemm600004.china.huawei.com (unknown [7.193.23.242]) by mail.maildlp.com (Postfix) with ESMTPS id 24AFE140124; Tue, 26 Mar 2024 20:15:19 +0800 (CST) Received: from [10.67.121.59] (10.67.121.59) by kwepemm600004.china.huawei.com (7.193.23.242) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.35; Tue, 26 Mar 2024 20:15:18 +0800 Message-ID: <1e227884-348c-25eb-24c5-8ce19137173d@huawei.com> Date: Tue, 26 Mar 2024 20:15:17 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH 0/2] introduce PM QoS interface To: =?UTF-8?Q?Morten_Br=c3=b8rup?= , CC: , , , , , References: <20240320105529.5626-1-lihuisong@huawei.com> <98CBD80474FA8B44BF855DF32C47DC35E9F315@smartserver.smartshare.dk> <9d896d8e-e624-6501-5c2d-d6b664c9a15d@huawei.com> <98CBD80474FA8B44BF855DF32C47DC35E9F31C@smartserver.smartshare.dk> <9e85c849-99d9-2d81-b79f-28fc49a54e4f@huawei.com> <98CBD80474FA8B44BF855DF32C47DC35E9F327@smartserver.smartshare.dk> <7378ca2b-b6f3-815c-1bbf-4765dffc0134@huawei.com> <98CBD80474FA8B44BF855DF32C47DC35E9F32E@smartserver.smartshare.dk> From: "lihuisong (C)" In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35E9F32E@smartserver.smartshare.dk> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.121.59] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To kwepemm600004.china.huawei.com (7.193.23.242) X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org 在 2024/3/26 16:27, Morten Brørup 写道: >> From: lihuisong (C) [mailto:lihuisong@huawei.com] >> Sent: Tuesday, 26 March 2024 03.12 >> >> 在 2024/3/22 20:35, Morten Brørup 写道: >>>> From: lihuisong (C) [mailto:lihuisong@huawei.com] >>>> Sent: Friday, 22 March 2024 09.54 > [...] > >>>> For the case need PM QoS in DPDK, I think, it is better to set cpu >>>> latency to zero to prevent service thread from the deeper the idle >> state. >>> It would defeat the purpose (i.e. not saving sufficient amounts of >> power) if the CPU cannot enter a deeper idle state. >> Yes, it is not good for power. >> AFAIS, PM QoS is just to decrease the influence for performance. >> Anyway, if we set to zero, system can be into Cstates-0 at least. >>> Personally, I would think a wake-up latency of up to 10 microseconds >> should be fine for must purposes. >>> Default Linux timerslack is 50 microseconds, so you could also use >> that value. >> How much CPU latency is ok. Maybe, we can give the decision to the >> application. > Yes, the application should decide the acceptable worst-case latency. > >> Linux will collect all these QoS request and use the minimum latency. >> what do you think, Morten? > For the example application, you could use a value of 50 microseconds and refer to this value also being the default timerslack in Linux. There is a description for "/proc//timerslack_ns" in Linux document [1] " This file provides the value of the task’s timerslack value in nanoseconds. This value specifies an amount of time that normal timers may be deferred in order to coalesce timers and avoid unnecessary wakeups. This allows a task’s interactivity vs power consumption tradeoff to be adjusted. " I cannot understand what the relationship is between the timerslack in Linux and cpu latency to wake up. It seems that timerslack is just to defer the timer in order to coalesce timers and avoid unnecessary wakeups. And it has not a lot to do with the CPU latency which is aimed to avoid task to enter deeper idle state and satify application request. >