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=-10.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 73544C433E6 for ; Fri, 28 Aug 2020 11:19:53 +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 3D5A0207DF for ; Fri, 28 Aug 2020 11:19:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="irDWIYw8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3D5A0207DF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.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-Type: Content-Transfer-Encoding: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=IY0KOUvyzhJfvBlOBgDi9E1/c5LfCHVD2dtezRGEytk=; b=irDWIYw8jiuE6RxyZ5CocMAnI ffRu5yS4wXYkPXLE/k1BGPtSZ+2udKlvhy2aQdpDDaGtqaQnYArWOyuYbm+lIj2SGOGsCryDc+Qdn +Ji0Cb5T3oIShI1A3yYUP4eaeqgFOWA0jn/mwv4J/VrDtkTyapLn0/OlQ7qot1MKvUHtTOimhSkGb VDOMTJZlR2Z9iT+J/NhJPWlzRho/plhhAKyKRTybUe7tyZ3ilq7lKotxYJ+MPAMQRzAwB5i+RudB7 BSm1f7rXYnG5xxVLmUCgZJ4umcLg23NFSqn6Xo4GGhAC0wdOhjcZMrrgB17Z9OGaUhKNaPJLExv/w GJnZ/C+Fg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kBcOr-0003vO-Eh; Fri, 28 Aug 2020 11:18:29 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kBcOo-0003uu-TN for linux-arm-kernel@lists.infradead.org; Fri, 28 Aug 2020 11:18:27 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6524631B; Fri, 28 Aug 2020 04:18:24 -0700 (PDT) Received: from [10.57.40.122] (unknown [10.57.40.122]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 48BC73F66B; Fri, 28 Aug 2020 04:18:23 -0700 (PDT) Subject: Re: [PATCH] iommu/arm-smmu-v3: add tracepoints for cmdq_issue_cmdlist To: "Song Bao Hua (Barry Song)" , Will Deacon References: <20200827093351.15244-1-song.bao.hua@hisilicon.com> <20200828102927.GA30391@willie-the-truck> From: Robin Murphy Message-ID: <9acf1acf-19fb-26db-e908-eb4d4c666bae@arm.com> Date: Fri, 28 Aug 2020 12:18:17 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200828_071827_049308_2B57EF0D X-CRM114-Status: GOOD ( 24.89 ) 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" , "joro@8bytes.org" , "linux-arm-kernel@lists.infradead.org" , Linuxarm Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-08-28 12:02, Song Bao Hua (Barry Song) wrote: > > >> -----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); > ... > } If you only want to measure entry and exit of one specific function, though, can't the function graph tracer already do that? Otherwise, pursuing optprobes sounds like a worthwhile thing to do since that should benefit everyone, rather than just the 6 people on the planet who might care about arm_smmu_issue_cmdlist(). As long as it doesn't involve whole new ISA extensions like the RISC-V proposal ;) Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel