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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 DFD71C1B0E3 for ; Mon, 14 Dec 2020 10:02:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9E2F322AAD for ; Mon, 14 Dec 2020 10:02:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405038AbgLNKBl (ORCPT ); Mon, 14 Dec 2020 05:01:41 -0500 Received: from foss.arm.com ([217.140.110.172]:45452 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391938AbgLNKBR (ORCPT ); Mon, 14 Dec 2020 05:01:17 -0500 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 CF26030E; Mon, 14 Dec 2020 02:00:30 -0800 (PST) Received: from [10.57.63.94] (unknown [10.57.63.94]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F3BE13F66E; Mon, 14 Dec 2020 02:00:28 -0800 (PST) Subject: Re: [RFC 09/11] coresight: etm-perf: Disable the path before capturing the trace data To: Mathieu Poirier Cc: Anshuman Khandual , linux-arm-kernel@lists.infradead.org, coresight@lists.linaro.org, linux-kernel@vger.kernel.org, mike.leach@linaro.org, Al Grant References: <1605012309-24812-1-git-send-email-anshuman.khandual@arm.com> <1605012309-24812-10-git-send-email-anshuman.khandual@arm.com> <2019e06d-65e1-fee8-f75d-bfa5750d2458@arm.com> <20201211203126.GA1921322@xps15> From: Suzuki K Poulose Message-ID: Date: Mon, 14 Dec 2020 10:00:27 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <20201211203126.GA1921322@xps15> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/11/20 8:31 PM, Mathieu Poirier wrote: > On Fri, Nov 27, 2020 at 10:32:28AM +0000, Suzuki K Poulose wrote: >> On 11/10/20 12:45 PM, Anshuman Khandual wrote: >>> perf handle structure needs to be shared with the TRBE IRQ handler for >>> capturing trace data and restarting the handle. There is a probability >>> of an undefined reference based crash when etm event is being stopped >>> while a TRBE IRQ also getting processed. This happens due the release >>> of perf handle via perf_aux_output_end(). This stops the sinks via the >>> link before releasing the handle, which will ensure that a simultaneous >>> TRBE IRQ could not happen. >> >> Or in other words : >> >> We now have : >> >> update_buffer() >> >> perf_aux_output_end(handle) >> >> ... >> disable_path() >> >> This is problematic due to various reasons : >> >> 1) The semantics of update_buffer() is not clear. i.e, whether it >> should leave the "sink" "stopped" or "disabled" or "active" > > I'm a little confused by the above as the modes that apply here are > CS_MODE_DISABLED and CS_MODE_PERF, so I'll go with those. Let me know if you > meant something else. Sorry, I think it is a bit confusing. stopped => Sink is in stopped HW state, but the software mode is not changed (i.e, could be PERF or SYSF) disabled => Sink is in stopped hw state, the software mode is DISABLED active => Sink is active and flushing trace, with respective mode (PERF vs SYSFS). > > So far ->update_buffer() doesn't touch drvdata->mode and as such it is still set > to CS_MODE_PERF when the update has completed. > >> >> 2) This breaks the recommended trace collection sequence of >> "flush" and "stop" from source to the sink for trace collection. >> i.e, we stop the source now. But don't flush the components >> from source to sink, rather we stop and flush from the sink. >> And we flush and stop the path after we have collected the >> trace data at sink, which is pointless. > > The above assesment is correct. Fixing it though has far reaching ramifications > that go far beyond the scope of this patch. > >> >> 3) For a sink with IRQ handler, if we don't stop the sink with >> update_buffer(), we could have a situation : >> >> update_buffer() >> >> perf_aux_outpuf_end(handle) # handle is invalid now >> >> -----------------> IRQ -> irq_handler() >> perf_aux_output_end(handle) # Wrong ! >> >> >> disable_path() > > That's the picture of the issue I had in my head when looking at the code - > I'm glad we came to the same conclusion. > >> >> The sysfs mode is fine, as we defer the trace collection to disable_path(). >> >> The proposed patch is still racy, as we could still hit the problem. >> >> So, to avoid all of these situations, I think we should defer the the >> update_buffer() to sink_ops->disable(), when we have flushed and stopped >> the all the components upstream and avoid any races with the IRQ >> handler. >> >> i.e, >> >> source_ops->stop(csdev); >> >> disable_path(handle); // similar to the enable_path >> >> >> sink_ops->disable(csdev, handle) >> { >> /* flush & stop */ >> >> /* collect trace */ >> perf_aux_output_end(handle, size); >> } > > That is one solution. The advantage here is that it takes care of the > flusing problem you described above. On the flip side it is moving a lot of > code around, something that is better to do in another set. > > Another solution is to disable the TRBE IRQ in ->udpate_buffer(). The ETR does > the same kind of thing with tmc_flush_and_stop(). I don't know how feasible > that is but it would be a simple solution for this set. Properly flushing the > pipeline could be done later. I'm fine with either approach. Agreed. I think this is reasonable forthis set. i.e, leave the hardware disabled. We could do the proper solution above as a separate series, to keep the changes incremental. Kind regards Suzuki