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=-10.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 2E8E0C433ED for ; Tue, 27 Apr 2021 10:02:54 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 8B3F8613C5 for ; Tue, 27 Apr 2021 10:02:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8B3F8613C5 Authentication-Results: mail.kernel.org; dmarc=fail (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=desiato.20200630; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:Cc:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=S6TyVzcvCPAfz8PW85XW2WI7fMBPTdfIfYnFL9Uk9Ko=; b=cKCgpGJU9xoIhZR/C7FcIN7nP S7iWTqfJJFT5xjzWaKCW2mpQqrv1KKEmlOtDc0J7iC/S2TxhXjcg5AJM3xTS/2kBPxtqGjsobCHHe wnmCGAse4Sv42GOgfHA7OrDWT+WpAV+HsdKzv98ewdI4dKmyvS6ug39/+fc7d4o77PQO/6lehr6+Y SAkXjAsXBKKEDWdP/7rKNIDXGvBQv4b8Mueaj0KJOrdfP0KhswOevKyKUIxT0giubEIsgG95du8D2 g4x3yoBT+l8iffyERHjYbCKvfiMehdZ1u0mOcFbChSaBffqfNepmv7Y1rYQTkYbKWiN+SPsUeH1cF Xbs32QXgg==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lbKWi-001HyE-De; Tue, 27 Apr 2021 10:01:08 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lbKWf-001Hxw-62 for linux-arm-kernel@desiato.infradead.org; Tue, 27 Apr 2021 10:01:05 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To: Subject:Sender:Reply-To:Content-ID:Content-Description; bh=SHyS8te8uVyEWzBQs8wlcAaV67EqtqMeuItWu5vVeAQ=; b=NoBy0yc+k7uZJyj3d5rT6iJLha xknu90RrOgGOJG/FD/f1rgrAX3PCAPcNb5h9ESZaIIeJQGhEAPcVjzNsJHWuMpKAZmYkku+6nA5Vn 5AyNjD15fjGfHvHOhaX58AXZooIii/OPeoUex9wUpFJFFDNHpbEaNEEueMzXcqzJ+O6/s7wexAX98 8MP8qjeZBXLpdMHcGJsuLb8La5ws53qGs2VzUowLL80ePP400YndN7NUdrN1CEnpJMannbt5mrNyg Vq4DM6wUNHpOfOS9sVozXW1a8c0yqYmCtutlLFrgJ6N8pbQL3Ol8aECEEl3RGsWvC8gyy+j6/vqSP rgxSwryQ==; Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lbKWb-00GbRl-Rr for linux-arm-kernel@lists.infradead.org; Tue, 27 Apr 2021 10:01:03 +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 4425BD6E; Tue, 27 Apr 2021 03:00:54 -0700 (PDT) Received: from [10.57.67.211] (unknown [10.57.67.211]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EDB4B3F694; Tue, 27 Apr 2021 03:00:52 -0700 (PDT) Subject: Re: [PATCH 1/4] coresight: tmc-etr: Advance buffer pointer in sync buffer. To: Leo Yan Cc: Daniel Kiss , mathieu.poirier@linaro.org, mike.leach@linaro.org, coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, denik@google.com, Branislav Rankov References: <20210421120413.3110775-1-daniel.kiss@arm.com> <20210421120413.3110775-2-daniel.kiss@arm.com> <20210427034531.GA328795@leoy-ThinkPad-X240s> From: Suzuki K Poulose Message-ID: Date: Tue, 27 Apr 2021 11:00:51 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: <20210427034531.GA328795@leoy-ThinkPad-X240s> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210427_030102_327701_C12BA11D X-CRM114-Status: GOOD ( 31.40 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 27/04/2021 04:45, Leo Yan wrote: > On Mon, Apr 26, 2021 at 11:40:44AM +0100, Suzuki Kuruppassery Poulose wrote: > > [...] > >>> @@ -1442,7 +1442,7 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf, >>> { >>> long bytes; >>> long pg_idx, pg_offset; >>> - unsigned long head = etr_perf->head; >>> + unsigned long head; >>> char **dst_pages, *src_buf; >>> struct etr_buf *etr_buf = etr_perf->etr_buf; >>> @@ -1465,7 +1465,7 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf, >>> bytes = tmc_etr_buf_get_data(etr_buf, src_offset, to_copy, >>> &src_buf); >>> if (WARN_ON_ONCE(bytes <= 0)) >>> - break; >>> + return; >>> bytes = min(bytes, (long)(PAGE_SIZE - pg_offset)); >>> memcpy(dst_pages[pg_idx] + pg_offset, src_buf, bytes); >>> @@ -1483,6 +1483,7 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf, >>> /* Move source pointers */ >>> src_offset += bytes; >>> } >>> + etr_perf->head = (pg_idx << PAGE_SHIFT) + pg_offset; >> >> >> Looking at this patch, I feel the driver is doing a couple wrong things >> already. >> >> 1) We initialise etr_perf->head every time the ETR enable is called, >> irrespective of whether we actually try to enable the Hardware. e.g, >> >> etm_0 on -> .. -> enable_etr : >> etr_perf->head = >> enable_hw() >> >> emt_1 on -> ... -> enable_etr: >> etr_perf->head = >> already_enabled, skip enable_hw() >> >> etm_2 on -> ... -> enable_etr: >> etr_perf->head = >> already_enable, skip enable_hw()... >> >> >> This doesn't look correct as we don't know which handle is going to get the >> data. This looks pointless. > > I'd like to convert mapping into below diagram (for system wide trace): > > CPU0: AUX RB (perf_output_handle_0) -> etr_perf -> +---------+ > CPU1: AUX RB (perf_output_handle_1) -> etr_perf -> | etr_buf | > CPU2: AUX RB (perf_output_handle_2) -> etr_perf -> | | > CPU3: AUX RB (perf_output_handle_3) -> etr_perf -> +---------+ > To make it more clear: CPU0: AUX RB (perf_output_handle_0) -> etr_perf0 -> +---------+ CPU1: AUX RB (perf_output_handle_1) -> etr_perf1 -> |etr_buf0 | CPU2: AUX RB (perf_output_handle_2) -> etr_perf2 -> | | CPU3: AUX RB (perf_output_handle_3) -> etr_perf3 -> +---------+ > Simply to say, there have two layers for controlling ring buffer, one > layer is for perf AUX ring buffer, it mainly uses the structure > perf_output_handle to manage the ring buffer. And in the ETR driver, > it uses structure etr_perf to manage the header pointer for copying > data into ETR buffer (tagged as "etr_buf"). > > ETR buffer is the single one, but the structures "perf_output_handle" > and "etr_perf" are per CPU. We have multiple copies for the headers and minor Correction, they are "per-event" to be precise. And there are events per-CPU in a system wide mode or task mode (but not per-thread mode). So, you are correct > tails to manage a single buffer, but the problem is these multiple > copies have not been synced with each other. > >> 2) Even more problematic is where we copy the AUX buffer content to. >> As mentioned above, we don't know which handle is going to be the last >> one to consume and we have a "etr_perf->head" that came from one of the >> handles and the "pages" that came from the first handle which created a >> etr_perf buffer. In sync_perf_buffer() we copy the hardware buffers to >> the "pages" (say of handle_0) with "etr_perf->head" (which could be from >> any other handle, say handle_2) and then we could return the number of bytes >> copied, which then is used to update the last handle (could be say >> handle_3), where there is no actual data copied. This is not valid and am relieved that the driver is correct. The assumption that there is only one etr_perf per ETR is incorrect as pictured above. >> >> To fix all of these issues, we must >> 1) Stop using etr_perf->head, and instead use the handle->head where we are >> called update_buffer on. >> >> 2) Keep track of the "pages" that belong to a given "handle" and then use >> those pages to copy the data to the current handle we are called to update >> the buffer on. > > The "pages" are only allocated once, even they are attached to multiple > handles. I think the right way is to use the single structure I assume you mean the pages in the etr_buf and not etr_perf right ? > "etr_perf" and single "perf_output_handle" to manage the "pages", IOW, > if there have single buffer, then we just use one copy of header and > tail to manage it. I think this is not needed and the way we do things are fine and the patch as such looks correct to me. The perf_output_handle is per-event and nothing that we can combine with. etr_perf captures what the "ouput_handle" stands for and is something necessary for syncing the buffer. Now coming back to this patch, I understand that the sync_perf could be called with the polling patches multiple times. But don't we do a perf_output_handle_end() each of the time we wake up ? (I haven't looked at the later patches yet). I would expect: perf_aux_output_begin() -> update the etr_perf-> head when we sync the buffer, we do : Poll-> sync_buffer-> perf_aux_output_end() and perf_aux_output_begin() -> update etr_perf->head. Kind regards Suzuki _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel