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 0B34FC433F5 for ; Tue, 12 Oct 2021 08:20:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9FBD60C41 for ; Tue, 12 Oct 2021 08:19:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234071AbhJLIV4 (ORCPT ); Tue, 12 Oct 2021 04:21:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:52084 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232541AbhJLIVz (ORCPT ); Tue, 12 Oct 2021 04:21:55 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5C27A6101D; Tue, 12 Oct 2021 08:19:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1634026794; bh=lDPufYSiKyvGGDrYONfULzGOTQL591ZiKQDt8MPRrw8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EbhrCQT6mNhvQPiAFl8cNGZj7me7jYjv8/NCbzUy/aKo5RfWSXhn4M4I78GlMhNRN pruhFBcjfGZcQkqF+4MPON1fwgpXBNmSoDzYF/fF4/0mYUDH3g6ZXPuATahOpCcOgq +q0S6w9teF4Kw+i2PtOTccVI0E/N4LIvGostQHdf+3j1mApKvEZyDRr7DlVJHOTpCE nx5qm85PGJTFzlTIBreR9gDbjD/K+a/s0oVk3UIkQOQh6bgoQImCGJ4ckusQxKlJ/D eAqfvgiMXVFt82AgIP8Y/awQPdli5FYtnaEAdAkxd4wg6pPT4RTUZVzqLF0EI5mlCy rDeHnI04DOUdw== Date: Tue, 12 Oct 2021 09:19:48 +0100 From: Will Deacon To: German Gomez Cc: Leo Yan , 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: <20211012081948.GA5156@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <377b54ef-b9c0-9cfc-ef0c-0187d7c493cc@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On Mon, Oct 11, 2021 at 04:55:37PM +0100, German Gomez wrote: > Hi Leo, > > 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. > > An alternative way we considered to simplify the patch is to change the > logic inside the find_snapshot callback so that it records the entire > contents of the aux buffer every time. > > What do you think? What does intel-pt do? Will