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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 BE0E1C352A3 for ; Mon, 10 Feb 2020 11:56:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8826D20733 for ; Mon, 10 Feb 2020 11:56:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="RRLuCy0R" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727477AbgBJL4Y (ORCPT ); Mon, 10 Feb 2020 06:56:24 -0500 Received: from mail26.static.mailgun.info ([104.130.122.26]:64272 "EHLO mail26.static.mailgun.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727061AbgBJL4Y (ORCPT ); Mon, 10 Feb 2020 06:56:24 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1581335783; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: Cc: To: References: Subject: Sender; bh=msK0pnyL6OkobNKSG9pUtr6X/d0ixckiXExfRYSIcCI=; b=RRLuCy0R3rxcWX0gdkz06XQh/yGTq0yOKNSliyf9ausQU02rU+1ZhK7j7aNuXN4Ye9qiNtVH 5vVZ4Azclk38GeArmthH0O1XkjxW6ihNl6se6mQVaHVqx9WjyRuGAtPZTV1DH4uaLZIiGZqT ATw/y+LJil3JHy8l91CVTerxbtI= X-Mailgun-Sending-Ip: 104.130.122.26 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by mxa.mailgun.org with ESMTP id 5e4144e6.7ff4d49b7b58-smtp-out-n01; Mon, 10 Feb 2020 11:56:22 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 1BA03C4479C; Mon, 10 Feb 2020 11:56:21 +0000 (UTC) Received: from [10.252.218.68] (blr-c-bdr-fw-01_GlobalNAT_AllZones-Outside.qualcomm.com [103.229.19.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: gkohli) by smtp.codeaurora.org (Postfix) with ESMTPSA id CA6BBC43383; Mon, 10 Feb 2020 11:56:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org CA6BBC43383 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=none smtp.mailfrom=gkohli@codeaurora.org Subject: Query: Regarding Notifier chain callback debugging or profiling References: <82d5b63e-4ae6-fb5f-8a1c-2d5755db2638@codeaurora.org> To: akpm@linux-foundation.org, linux-kernel , Greg KH , tglx@linutronix.de Cc: linux-arm-msm@vger.kernel.org, neeraju@codeaurora.org From: Gaurav Kohli X-Forwarded-Message-Id: <82d5b63e-4ae6-fb5f-8a1c-2d5755db2638@codeaurora.org> Message-ID: <6e077b43-6c9e-3f4e-e079-db438e36a4eb@codeaurora.org> Date: Mon, 10 Feb 2020 17:26:16 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <82d5b63e-4ae6-fb5f-8a1c-2d5755db2638@codeaurora.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, In Linux kernel, everywhere we are using notification chains to notify for any kernel events, But we don't have any debugging or profiling mechanism to know which callback is taking time or currently we are stuck on which call back(without dumps it is difficult to say for last problem) Below are the few ways, which we can implement to profile callback on need basis: 1) Use trace event before and after callback: static int notifier_call_chain(struct notifier_block **nl, unsigned long val, void *v, int nr_to_call, int *nr_calls) { int ret = NOTIFY_DONE; struct notifier_block *nb, *next_nb; + trace_event for entry of callback ret = nb->notifier_call(nb, val, v); + trace_event for exit of callback } return ret; } 2) Or use pr_debug instead of trace_event 3) Both of the above approach has certain problems, like it will dump callback for each notifier chain, which might flood trace buffer or dmesg. So we can use bool variable to control that and dump the required notification chain only. Some thing like below we can use: struct srcu_notifier_head { struct mutex mutex; struct srcu_struct srcu; struct notifier_block __rcu *head; + bool debug_callback; }; static int notifier_call_chain(struct notifier_block **nl, unsigned long val, void *v, - int nr_to_call, int *nr_calls) + int nr_to_call, int *nr_calls, bool debug_callback) { int ret = NOTIFY_DONE; struct notifier_block *nb, *next_nb; @@ -526,6 +526,7 @@ void srcu_init_notifier_head(struct srcu_notifier_head *nh) if (init_srcu_struct(&nh->srcu) < 0) BUG(); nh->head = NULL; + nh->debug_callback = false; -> by default it would be false for every notifier chain. 4) we can also think of something pre and post function, before and after each callback, And we can enable only for those who wants to profile. Please let us what approach we can use, or please suggest some debugging mechanism for the same. Regards Gaurav -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.