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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 380EDC67790 for ; Wed, 25 Jul 2018 09:50:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D9E3220685 for ; Wed, 25 Jul 2018 09:50:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D9E3220685 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-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728806AbeGYLBo (ORCPT ); Wed, 25 Jul 2018 07:01:44 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:35430 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728651AbeGYLBn (ORCPT ); Wed, 25 Jul 2018 07:01:43 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BD1C315A2; Wed, 25 Jul 2018 02:50:48 -0700 (PDT) Received: from [10.37.10.30] (unknown [10.37.10.30]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4D0DC3F237; Wed, 25 Jul 2018 02:50:47 -0700 (PDT) Subject: Re: [PATCH v2 09/10] coresight: perf: Remove set_buffer call back To: Mathieu Poirier Cc: linux-arm-kernel , Linux Kernel Mailing List , Robert Walker , Mike Leach , coresight@lists.linaro.org References: <1531847501-22226-1-git-send-email-suzuki.poulose@arm.com> <1531847501-22226-10-git-send-email-suzuki.poulose@arm.com> <20180719203630.GC9421@xps15> <2f646ecb-8150-d184-4d94-d2855ddfafd1@arm.com> From: Suzuki K Poulose Message-ID: Date: Wed, 25 Jul 2018 10:51:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/24/2018 09:08 PM, Mathieu Poirier wrote: > On Mon, 23 Jul 2018 at 16:27, Suzuki K Poulose wrote: >> >> Mathieu, >> >> On 07/23/2018 07:22 PM, Mathieu Poirier wrote: >>> On Fri, 20 Jul 2018 at 03:04, Suzuki K Poulose wrote: >>>> >>>> Mathieu, >>>> >>>> On 19/07/18 21:36, Mathieu Poirier wrote: >>>>> On Tue, Jul 17, 2018 at 06:11:40PM +0100, Suzuki K Poulose wrote: >>>>>> In coresight perf mode, we need to prepare the sink before >>>>>> starting a session, which is done via set_buffer call back. >>>>>> We then proceed to enable the tracing. If we fail to start >>>>>> the session successfully, we leave the sink configuration >>>>>> unchanged. This was fine for the existing backends as they >>>>>> don't have any state associated with the buffers. But with >>>>>> ETR, we need to keep track of the buffer details and need >>>>>> to be cleaned up if we fail. In order to make the operation >>>>>> atomic and to avoid yet another call back, we get rid of >>>>>> the "set_buffer" call back and pass the buffer details >>>>>> via enable() call back to the sink. >>>>> >>>>> Suzuki, >>>>> >>>>> I'm not sure I understand the problem you're trying to fix there. From the >>>>> implementation of tmc_enable_etr_sink_perf() in the next patch, wouldn't the >>>>> same result been achievable using a callback? >>>> >>>> We can definitely achieve the results using "set_buffer". But for ETR, >>>> we track the "perf_buf" in drvdata->perf_data when we do "set_buffer". >>>> But if we failed to enable_path(), we leave the drvdata->perf_data >>>> and doesn't clean it up. Now when another session is about to set_buf, >>>> we check if perf_data is empty and WARNs otherwise. >>>> Because we can't be sure if it belongs to an abandoned session or >>>> another active session and we completely messed somewhere in the driver. >>>> So, we need a clear_buffer call back if the enable fails, something >>>> not really worth. Anyways, there is no point in separating set_buffer >>>> and enabling the sink, as the error handling becomes cumbersome as explained >>>> above. >>>> >>>>> >>>>> I'm fine with this patch and supportive of getting rid of callbacks if we can, I >>>>> just need to understand the exact problem you're after. From looking a your >>>>> code (and the current implementation), if we succeed in setting the memory for >>>>> the sink but fail in any of the subsequent steps i.e, enabling the rest of the >>>>> compoment on the path or the source, the sink is left unchanged. >>>> >>>> Yes, thats right. And we should WARN (which I missed in this version) if >>>> there is a perf_data already for a disabled ETR. Please see my response to the >>>> next patch. >>> >>> The changelog for this patch states the following: "But with ETR, we >>> need to keep track of the buffer details and need to be cleaned up if >>> we fail." >>> >>> I did a deep dive in the code and in the current implementation if the >>> source fails to be enabled in etm_event_start() the path and the sink >>> remains unchanged. With your patchset this get fixed because a goto >>> was added to disable the path when such condition occur. As such each >>> component in the path will see its ->disable() callback invoked. In >>> tmc_disable_etr_sink(), drvdata->perf_data is set to NULL in >>> tmc_etr_disable_hw(), so the cleanup on error condition is done >>> properly. As such we wouldn't need a clean_buffer() callback. >> >> All of this is right. But we still have a case. e.g, if the ETR is >> enabled in sysfs mode, coresight_enable_path() will fail after we >> have set the buffer. And since we don't try to disable the path >> when we fail at SINK (which is the right thing to do, as we could >> be potentially disabling the ETR operated in sysfs mode), we leave >> the perf_data around. And the next session finds a non-empty data. > > We are in total agreement :o) > > All I hoping for is to see the sentence "But with ETR, we need to keep > track of the buffer details and need to be cleaned up if we fail." > removed from the changelog. To me that sounds like you're adding > cleanup work in enable() which isn't the case. On the flip side you > are making the sink configuration atomic and that is the important > part. :-), I will update the change log accordingly. > >> >>> >>> As I said I'm in favour of removing the set_buffer() callback but I >>> wouldn't associated it with ETR state cleanup. If the code can be >>> rearranged in a way that code can be removed then that alone is enough >>> to ju >>>>>> + if (coresight_enable_path(path, CS_MODE_PERF, handle)) >>>>> >>>>> Here we already have a handle on "event_data". As such I think this is what we >>>>> should feed to coresight_enable_path() rather than the handle. That way we >>>>> don't need to call etm_perf_sink_config(), we just use the data. >>>> >>>> The advantage of passing on the handle is, we could get all the way upto the >>>> "perf_event" for the given session. Passing the event_data will loose that >>>> information. >>>> >>>> i.e, perf_event-> |perf_ouput_handle | -> |event_data | -> sink_config >>>> | <-event | | | >>>> >>>> The purpose of the wrapper "etm_perf_sink_config()" is to abstract the way we >>>> handle the information under the event_data. i.e, if we decide to make some >>>> changes in the way we store event_data, we need to spill the changes every >>>> where. But the perf_ouput_handle has much more stable ABI than event_data, >>>> hence the choice of passing handle. >>> >>> I agree that etm_perf_sink_config() has value but it should take a >>> void * as parameter (i.e what gets returned from perf_get_aux()) >>> rather than a perf_output_handle *. >> >> Ok, did you mean : >> >> sink_config = etm_perf_sink_config(perf_get_aux(handle)); ? >> >> Or do you want to change the parameter passed to the enable_sink() as >> well ? > > I've been thinking further on this and keeping things the way you've > implemented them is probably best at this time. I'm currently adding > support for PMU HW configuration and in the end we may need the > information conveyed by event->hw.drv_config [1]. When it's all said > and done we can clean things up if need be. Ok. Thanks for the review. Cheers Suzuki