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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4D4D1C433F5 for ; Fri, 15 Oct 2021 12:33:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 24C626108E for ; Fri, 15 Oct 2021 12:33:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235571AbhJOMfv (ORCPT ); Fri, 15 Oct 2021 08:35:51 -0400 Received: from foss.arm.com ([217.140.110.172]:41970 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234372AbhJOMfv (ORCPT ); Fri, 15 Oct 2021 08:35:51 -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 4D9E1147A; Fri, 15 Oct 2021 05:33:44 -0700 (PDT) Received: from [10.57.73.178] (unknown [10.57.73.178]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A18913F70D; Fri, 15 Oct 2021 05:33:41 -0700 (PDT) Subject: Re: [PATCH 4/5] perf arm-spe: Implement find_snapshot callback To: Leo Yan Cc: Will Deacon , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, John Garry , Mathieu Poirier , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Mike Leach , linux-arm-kernel@lists.infradead.org, coresight@lists.linaro.org, James Clark References: <20210916154635.1525-1-german.gomez@arm.com> <20210916154635.1525-4-german.gomez@arm.com> <20210923135016.GG400258@leoy-ThinkPad-X240s> <20210923144048.GB603008@leoy-ThinkPad-X240s> <1c6a3a73-27dc-6673-7fe7-34bc7fcb0a68@arm.com> <20211004122724.GC174271@leoy-ThinkPad-X240s> <6b092f13-832f-5d1d-a504-aea96c81bf17@arm.com> <20211006095124.GC14400@leoy-ThinkPad-X240s> <377b54ef-b9c0-9cfc-ef0c-0187d7c493cc@arm.com> <20211013003916.GA130842@leoy-ThinkPad-X240s> <20211013075125.GA6701@willie-the-truck> From: German Gomez Message-ID: <35209d5c-6387-5248-ab61-a1e1cb0553de@arm.com> Date: Fri, 15 Oct 2021 13:33:39 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20211013075125.GA6701@willie-the-truck> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Hi Leo, Would you be ok with the current patch the way it is? In case it's of any help, I'm sharing the testing steps that James and I went through when testing this internally, if you want to add to it - Test that only a portion of the buffer is saved until there is a wraparound $ ./perf record -vvv -e arm_spe/period=148576/u -S -- taskset --cpu-list 0 stress --cpu 1 & while true; do sleep 0.2; killall -s USR2 perf; done - Test snapshot mode in CPU mode $ sudo ./perf record -vvv -C 0 -e arm_spe/period=148576/u -S -- taskset --cpu-list 0 stress --cpu 1 & - Test that auxtrace buffers correspond to an aux record - Test snapshot default sizes in sudo and user modes - Test small snapshot size $ ./perf record -vvv -e arm_spe/period=148576/u -S1000 -m16,16 -- taskset --cpu-list 0 stress --cpu 1 & If there are any concerns with the patches, please let me know and I will try to address them. Thanks, German On 13/10/2021 08:51, Will Deacon wrote: > On Wed, Oct 13, 2021 at 08:39:16AM +0800, Leo Yan wrote: >> On Mon, Oct 11, 2021 at 04:55:37PM +0100, German Gomez wrote: >>> On 06/10/2021 10:51, Leo Yan wrote: >>>> On Wed, Oct 06, 2021 at 10:35:20AM +0100, German Gomez wrote: >>>> >>>> [...] >>>> >>>>>> So simply say, I think the head pointer monotonically increasing is >>>>>> the right thing to do in Arm SPE driver. >>>>> I will talk to James about how we can proceed on this. >>>> Thanks! >>> I took this offline with James and, though it looks possible to patch >>> the SPE driver to have a monotonically increasing head pointer in order >>> to simplify the handling in the perf tool, it could be a breaking change >>> for users of the perf_event_open syscall that currently rely on the way >>> it works now. >> Here I cannot create the connection between AUX head pointer and the >> breakage of calling perf_event_open(). >> >> Could you elaborate what's the reason the monotonical increasing head >> pointer will lead to the breakage for perf_event_open()? > It's a user-visible change in behaviour, isn't it? Therefore we risk > breaking applications that rely on the current behaviour if we change it > unconditionally. > > Given that the driver has always worked like this and it doesn't sound like > it's the end of the world to deal with it in userspace (after all, it's > aligned with intel-pt), then I don't think we should change it. > > Will