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=-6.7 required=3.0 tests=BAYES_00, 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 744C6C433E2 for ; Fri, 28 Aug 2020 11:02:17 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (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 4498C207DF for ; Fri, 28 Aug 2020 11:02:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4498C207DF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=hisilicon.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 16790885B5; Fri, 28 Aug 2020 11:02:17 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id JpkZ2Y1yEZkU; Fri, 28 Aug 2020 11:02:15 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id CCC88885A0; Fri, 28 Aug 2020 11:02:15 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id B152AC016F; Fri, 28 Aug 2020 11:02:15 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) by lists.linuxfoundation.org (Postfix) with ESMTP id 0F3ACC0051 for ; Fri, 28 Aug 2020 11:02:14 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id E83AA228D5 for ; Fri, 28 Aug 2020 11:02:13 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id uiZIk3T9nlhh for ; Fri, 28 Aug 2020 11:02:11 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from huawei.com (szxga02-in.huawei.com [45.249.212.188]) by silver.osuosl.org (Postfix) with ESMTPS id 25FAD228BA for ; Fri, 28 Aug 2020 11:02:10 +0000 (UTC) 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 Cc: "iommu@lists.linux-foundation.org" , "robin.murphy@arm.com" , "linux-arm-kernel@lists.infradead.org" , Linuxarm X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" > -----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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu