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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 F18ADC433E7 for ; Mon, 12 Oct 2020 08:48:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A387D208FE for ; Mon, 12 Oct 2020 08:48:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602492517; bh=cCsb7DHMH1TLtqM3vgMHvWsrDmhMZmW/jNR9XvpQzko=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=KM15FZcMi0L6jl0VX0XUvD/pdCt92RnYuSbGqpQo6r1KigHw5Bay4U45GkvrSjcBs D1RUGXkiazid4eawqKbYe5vbimpHQjYFyHMrpeSdj8vUKOypY+JizU/feTJDd1vZq5 CBWou/VotpzCYeEW5ZxsAXehPMmvAWIMW8o/mmSk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727481AbgJLIsg (ORCPT ); Mon, 12 Oct 2020 04:48:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:35240 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726104AbgJLIsg (ORCPT ); Mon, 12 Oct 2020 04:48:36 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 125C020773; Mon, 12 Oct 2020 08:48:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602492515; bh=cCsb7DHMH1TLtqM3vgMHvWsrDmhMZmW/jNR9XvpQzko=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OS0H5doFjiXqph3ehhylpNM+q9XJrnGqdIN80pHFDByD3AYZc+DWrZJ4pSV/XkVci HJkzWO57y1hf/VyyeKlmezv5aJukU9xTC6f48H9O/OXC9O8+AhB9HKUkHz+FBtFZDe wZFlDx8TXms+Ig6pPm0j0vUlO046LgPdNbXZoZL8= Date: Mon, 12 Oct 2020 09:48:29 +0100 From: Will Deacon To: Michael Ellerman Cc: Peter Zijlstra , kan.liang@linux.intel.com, mingo@redhat.com, acme@kernel.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@redhat.com, eranian@google.com, ak@linux.intel.com, dave.hansen@intel.com, kirill.shutemov@linux.intel.com, benh@kernel.crashing.org, paulus@samba.org, David Miller Subject: Re: [PATCH V9 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE Message-ID: <20201012084829.GA1151@willie-the-truck> References: <20201001135749.2804-1-kan.liang@linux.intel.com> <20201001135749.2804-2-kan.liang@linux.intel.com> <20201009090927.GQ2611@hirez.programming.kicks-ass.net> <877drz1qbc.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <877drz1qbc.fsf@mpe.ellerman.id.au> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 10, 2020 at 12:28:39AM +1100, Michael Ellerman wrote: > Peter Zijlstra writes: > > Patch 4 makes it all far worse by exposing it to pretty much everybody. > > > > Now, I think we can fix at least the user mappings with the below delta, > > but if archs are using non-page-table MMU sizes we'll need arch helpers. > > > > ARM64 is in that last boat. > > I think we probably need it to be weak so we can provide our own > version. I guess the same thing applies to us, but I can't really tell how accurate this stuff needs to be for userspace. If it's trying to use the page-table configuration to infer properties of the TLB, that's never going to be reliable because the TLB can choose both to split and coalesce entries as long as software can't tell. Will