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=-7.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 A0F3CC433E2 for ; Fri, 28 Aug 2020 11:03:39 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 6DC0F20872 for ; Fri, 28 Aug 2020 11:03:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="ODIqdIZs" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6DC0F20872 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=hisilicon.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+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=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References:Message-ID:Date: Subject:To:From:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=oHHqauYk8zEdZJLCtvn0y5uQA/iw5atmUiZtcIKztuQ=; b=ODIqdIZsHejQY2UrDNn46+pWV DelF45cDZj7p1DENybMqLCJEZAdNLxJJU+N+hMP4yME61b24I+xw2od/sGhHTS/GFQAfvoV/F7bw1 VXQWvlnV7pT0PJmVdvGJzok0ytFQDWUMkn/qw6pWjPsgeyhi8tu7MboCNl1mvwqrlsWISzL7PLPCZ g4B+cxNyp1uuRLMkuvdjY9xnk1+bjP7EyPqZUxazD5RHam/ZMz6rICYbXD5qhAqyUnTgVH28vcM9/ P2o4Zj7gOfD62kuxbUKO5AQjew2NTDNiLaWjuwAXgnl+gRK9E+ae78wT5usFe+F8eEFJ6hoYQ8f3E DzF3dxjCw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kBc99-0001sV-1J; Fri, 28 Aug 2020 11:02:15 +0000 Received: from szxga02-in.huawei.com ([45.249.212.188] helo=huawei.com) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kBc96-0001rc-D5 for linux-arm-kernel@lists.infradead.org; Fri, 28 Aug 2020 11:02:13 +0000 Received: from DGGEMM406-HUB.china.huawei.com (unknown [172.30.72.55]) by Forcepoint Email with ESMTP id CDBDD3FC27EB8AD609B2; Fri, 28 Aug 2020 19:02:04 +0800 (CST) Received: from dggemi762-chm.china.huawei.com (10.1.198.148) by DGGEMM406-HUB.china.huawei.com (10.3.20.214) with Microsoft SMTP Server (TLS) id 14.3.487.0; Fri, 28 Aug 2020 19:02:04 +0800 Received: from dggemi761-chm.china.huawei.com (10.1.198.147) by dggemi762-chm.china.huawei.com (10.1.198.148) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1913.5; Fri, 28 Aug 2020 19:02:04 +0800 Received: from dggemi761-chm.china.huawei.com ([10.9.49.202]) by dggemi761-chm.china.huawei.com ([10.9.49.202]) with mapi id 15.01.1913.007; Fri, 28 Aug 2020 19:02:04 +0800 From: "Song Bao Hua (Barry Song)" To: Will Deacon Subject: RE: [PATCH] iommu/arm-smmu-v3: add tracepoints for cmdq_issue_cmdlist Thread-Topic: [PATCH] iommu/arm-smmu-v3: add tracepoints for cmdq_issue_cmdlist Thread-Index: AQHWfFWUhbwMm9rWP0CSbrIWukW28qlMzW6AgACF0hA= Date: Fri, 28 Aug 2020 11:02:04 +0000 Message-ID: References: <20200827093351.15244-1-song.bao.hua@hisilicon.com> <20200828102927.GA30391@willie-the-truck> In-Reply-To: <20200828102927.GA30391@willie-the-truck> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.126.200.243] MIME-Version: 1.0 X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200828_070212_720926_7DCAF994 X-CRM114-Status: GOOD ( 16.11 ) 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: "iommu@lists.linux-foundation.org" , "robin.murphy@arm.com" , "joro@8bytes.org" , "linux-arm-kernel@lists.infradead.org" , Linuxarm Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org > -----Original Message----- > From: Will Deacon [mailto:will@kernel.org] > Sent: Friday, August 28, 2020 10:29 PM > To: Song Bao Hua (Barry Song) > Cc: iommu@lists.linux-foundation.org; linux-arm-kernel@lists.infradead.org; > robin.murphy@arm.com; joro@8bytes.org; Linuxarm > Subject: Re: [PATCH] iommu/arm-smmu-v3: add tracepoints for > cmdq_issue_cmdlist > > On Thu, Aug 27, 2020 at 09:33:51PM +1200, Barry Song wrote: > > cmdq_issue_cmdlist() is the hotspot that uses a lot of time. This patch > > adds tracepoints for it to help debug. > > > > Signed-off-by: Barry Song > > --- > > * can furthermore develop an eBPF program to benchmark using this trace > > Hmm, don't these things have a history of becoming ABI? If so, I don't > really want them in the driver at all, sorry. Do other drivers overcome > this somehow? This kind of tracepoints mainly works as a low-overhead probe point for debug purpose. I don't think any application would depend on it. It is for debugging. And there are lots of tracepoints in other drivers even in iommu driver core and intel_iommu driver :-) developers use it in one of the below ways: 1. get trace print from the ring buffer by reading debugfs root@ubuntu:/sys/kernel/debug/tracing/events/arm_smmu_v3# echo 1 > enable # cat /sys/kernel/debug/tracing/trace_pipe -0 [058] ..s1 125444.768083: issue_cmdlist_exit: arm-smmu-v3.2.auto cmd number=1 sync=1 -0 [058] ..s1 125444.768084: issue_cmdlist_entry: arm-smmu-v3.2.auto cmd number=1 sync=1 -0 [058] ..s1 125444.768085: issue_cmdlist_exit: arm-smmu-v3.2.auto cmd number=1 sync=1 -0 [058] ..s1 125444.768165: issue_cmdlist_entry: arm-smmu-v3.2.auto cmd number=1 sync=1 -0 [058] ..s1 125444.768168: issue_cmdlist_exit: arm-smmu-v3.2.auto cmd number=1 sync=1 -0 [058] ..s1 125444.768169: issue_cmdlist_entry: arm-smmu-v3.2.auto cmd number=1 sync=1 -0 [058] ..s1 125444.768171: issue_cmdlist_exit: arm-smmu-v3.2.auto cmd number=1 sync=1 -0 [058] ..s1 125444.768259: issue_cmdlist_entry: arm-smmu-v3.2.auto cmd number=1 sync=1 ... This can replace printk with much much lower overhead. 2. add a hook function in tracepoint to do some latency measure and time statistics just like the eBPF example I gave after the commit log. Using it, I can get the histogram of the execution time of cmdq_issue_cmdlist(): nsecs : count distribution 0 -> 1 : 0 | | 2 -> 3 : 0 | | 4 -> 7 : 0 | | 8 -> 15 : 0 | | 16 -> 31 : 0 | | 32 -> 63 : 0 | | 64 -> 127 : 0 | | 128 -> 255 : 0 | | 256 -> 511 : 0 | | 512 -> 1023 : 58 | | 1024 -> 2047 : 22763 |****************************************| 2048 -> 4095 : 13238 |*********************** | I feel it is very common to do this kind of things for analyzing the performance issue. For example, to easy the analysis of softirq latency, softirq.c has the below code: asmlinkage __visible void __softirq_entry __do_softirq(void) { ... trace_softirq_entry(vec_nr); h->action(h); trace_softirq_exit(vec_nr); ... } > > Will Thanks Barry _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel