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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A7EFCE79A8 for ; Tue, 19 Sep 2023 17:01:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230010AbjISRBr (ORCPT ); Tue, 19 Sep 2023 13:01:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38954 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229772AbjISRBr (ORCPT ); Tue, 19 Sep 2023 13:01:47 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id AC102AD; Tue, 19 Sep 2023 10:01:41 -0700 (PDT) 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 590051FB; Tue, 19 Sep 2023 10:02:18 -0700 (PDT) Received: from [10.57.94.61] (unknown [10.57.94.61]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8187A3F5A1; Tue, 19 Sep 2023 10:01:39 -0700 (PDT) Message-ID: <3cc013bd-c85e-b28a-f921-d5593b3935a4@arm.com> Date: Tue, 19 Sep 2023 18:01:38 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH v2 5/5] hwtracing: hisi_ptt: Add dummy callback pmu::read() To: Yicong Yang , mathieu.poirier@linaro.org, jonathan.cameron@huawei.com, linux-kernel@vger.kernel.org Cc: yangyicong@hisilicon.com, alexander.shishkin@linux.intel.com, helgaas@kernel.org, linux-pci@vger.kernel.org, prime.zeng@hisilicon.com, linuxarm@huawei.com, hejunhao3@huawei.com References: <20230914112223.27165-1-yangyicong@huawei.com> <20230914112223.27165-6-yangyicong@huawei.com> <73655f9b-9ea4-cb46-d712-20f1c4ac7c95@arm.com> <75b93d15-f099-5d17-caa9-94b0390773cf@huawei.com> From: Suzuki K Poulose In-Reply-To: <75b93d15-f099-5d17-caa9-94b0390773cf@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 19/09/2023 14:03, Yicong Yang wrote: > On 2023/9/15 20:53, Suzuki K Poulose wrote: >> On 14/09/2023 12:22, Yicong Yang wrote: >>> From: Junhao He >>> >>> When start trace with perf option "-C $cpu" and immediately stop it >>> with SIGTERM or others, the perf core will invoke pmu::read() while >>> the driver doesn't implement it. Add a dummy pmu::read() to avoid >>> any issues. >> >> What issues are we talking about here ? Shouldn't the core perf >> skip the call, if pmu::read() is not available ? >> > > Actually no, the core doesn't check it. So I think that's why some PMUs > like SPE implements a dummy pmu::read() callback. Otherwise we'll > dereference a NULL pointer. > > Currently we only met this on emulated platforms with very slow CPUs, > follow the instructions in the commit above. Ok, then it calls for a Fixes tag. Please tag it to the commit that introduced the PMU. Suzuki