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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 03D79C433F5 for ; Wed, 22 Sep 2021 10:17:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DBF9E60F21 for ; Wed, 22 Sep 2021 10:17:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234914AbhIVKSr (ORCPT ); Wed, 22 Sep 2021 06:18:47 -0400 Received: from foss.arm.com ([217.140.110.172]:46282 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234730AbhIVKSV (ORCPT ); Wed, 22 Sep 2021 06:18:21 -0400 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 2B33211B3; Wed, 22 Sep 2021 03:16:52 -0700 (PDT) Received: from [10.57.95.67] (unknown [10.57.95.67]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2327A3F719; Wed, 22 Sep 2021 03:16:49 -0700 (PDT) Subject: Re: [PATCH v2 14/17] coresight: trbe: Make sure we have enough space To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, maz@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, james.morse@arm.com, leo.yan@linaro.org, mike.leach@linaro.org, mathieu.poirier@linaro.org, will@kernel.org, lcherian@marvell.com, coresight@lists.linaro.org References: <20210921134121.2423546-1-suzuki.poulose@arm.com> <20210921134121.2423546-15-suzuki.poulose@arm.com> <60e75e7b-4a04-03d4-c861-88dd5fadef99@arm.com> From: Suzuki K Poulose Message-ID: Date: Wed, 22 Sep 2021 11:16:48 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <60e75e7b-4a04-03d4-c861-88dd5fadef99@arm.com> 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 22/09/2021 10:58, Anshuman Khandual wrote: > > > On 9/21/21 7:11 PM, Suzuki K Poulose wrote: >> The TRBE driver makes sure that there is enough space for a meaningful >> run, otherwise pads the given space and restarts the offset calculation >> once. But there is no guarantee that we may find space or hit "no space". > > So what happens currently when it neither finds the required minimum buffer > space for a meaningful run nor does it hit the "no space" scenario ? It tries once today and assumes that it will either hit : - No space OR - Enough space which is reasonable, given the minimum space needed is a few bytes. But this may no longer be true with other erratum workaround. > >> Make sure that we repeat the step until, either : >> - We have the minimum space >> OR >> - There is NO space at all. >> >> Cc: Anshuman Khandual >> Cc: Mathieu Poirier >> Cc: Mike Leach >> Cc: Leo Yan >> Signed-off-by: Suzuki K Poulose >> --- >> drivers/hwtracing/coresight/coresight-trbe.c | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c >> index 3373f4e2183b..02f9e00e2091 100644 >> --- a/drivers/hwtracing/coresight/coresight-trbe.c >> +++ b/drivers/hwtracing/coresight/coresight-trbe.c >> @@ -451,10 +451,14 @@ static unsigned long trbe_normal_offset(struct perf_output_handle *handle) >> * If the head is too close to the limit and we don't >> * have space for a meaningful run, we rather pad it >> * and start fresh. >> + * >> + * We might have to do this more than once to make sure >> + * we have enough required space. > > OR no space at all, as explained in the commit message. > Hence this comment needs an update. > >> */ >> - if (limit && ((limit - head) < trbe_min_trace_buf_size(handle))) { >> + while (limit && ((limit - head) < trbe_min_trace_buf_size(handle))) { >> trbe_pad_buf(handle, limit - head); >> limit = __trbe_normal_offset(handle); >> + head = PERF_IDX2OFF(handle->head, buf); > > Should the loop be bound with a retry limit as well ? No. We will eventually hit No-space as we keep on padding the buffer. Suzuki