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 1409CC433EF for ; Wed, 13 Oct 2021 09:42:38 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 DED78606A5 for ; Wed, 13 Oct 2021 09:42:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org DED78606A5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=wmF28wN5Z9dL+ho6MrUIdx0B5lW4WGtKrHwpNzO/enM=; b=ZQUxYOO8QMZjec FUR/VYEMBB7WGu+bLU4kaodbjFubylNW+OfSB94x8b5r+zWJvq1vrvsBgXbRVIHODViQfXSWRBm1q 1QKgpJXwXQI+7wivIOxvdQIx5ST8vc/ywCx6+x4nbSY0l5byBaQ7M16KiThlDw0RYlIZGzjr4kC2e x9kZVhQUL26KYR9J5YtOH0q6boZVvUlu5es22PM+IJrtP8ONuf8Nfspoud1xDFzcTDHczpY2LYz/I 7mlRu6B88iXOLiR5U/Je0zySD/zTTIztdOCPmAuPuN3z1vutfgOaLGq1yLrhHjwpWdCMPH+pS0o0G 600tclTy/PSLJKHzchuA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1maajJ-00FnSF-8Y; Wed, 13 Oct 2021 09:39:23 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1maZ2y-00FSVS-Tu for linux-arm-kernel@lists.infradead.org; Wed, 13 Oct 2021 07:51:34 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9E6A860E97; Wed, 13 Oct 2021 07:51:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1634111491; bh=jxBe3EdmOkp/uf/o/Y4dxlDbjXr7z5Jy5FzRlJAf0iU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vILv/kn38IFQtIG005rvJ82OGKrmrcTLR2kW4PIyv1aDZi0QVHFfftbMghZ3/V/cU sytZdYnQDpJkIr22aL4i2CKSyiWhy5IDVN1TTGBxh8lNlWHLtsK3RFeCrGrLchauNB bpezcsIyMd3Zd0w4jN/dscn89MfWjHYKsX80lR3njxJ+PlA9SzZJegZWwmlR6BsVGF Y0L2n4/Y/3NFjhsVkFM2Se4siag5ymMuHvobek6QusPZEu8VJwo/+d4CVr7qWFBDpv yl87VkqK+MMHWfJ2AG1ueH+v7bbZfWHjTqM+z4X84L3w9D5LqOtDSh3NwjwMyYDlZu rlhqmGpEfatFQ== Date: Wed, 13 Oct 2021 08:51:26 +0100 From: Will Deacon To: Leo Yan Cc: German Gomez , 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 Subject: Re: [PATCH 4/5] perf arm-spe: Implement find_snapshot callback Message-ID: <20211013075125.GA6701@willie-the-truck> 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> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20211013003916.GA130842@leoy-ThinkPad-X240s> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211013_005133_015552_6625506D X-CRM114-Status: GOOD ( 21.73 ) 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel