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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 A5DBBC32751 for ; Wed, 7 Aug 2019 11:13:11 +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 67BA521BF6 for ; Wed, 7 Aug 2019 11:13:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="eYvT+wqG" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 67BA521BF6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject: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=dsd7KEz3ox1VQXgCkaPviZTmrLeTSaHoarThl7mXwD0=; b=eYvT+wqGU+tvXR bl/BLfGQcbM0S3I5ogKw6m8xGymb3LYWohueJceOgB3zFNMTrXEARKUBbWdngAZTHg9bpMUOW16Fd ZyWPk3nznr+Bli0glKPlzeGQV5ERlZP+LiRcZ5o2twCXUIozuo6z9Zpoz5GPEJKJ9hUscvRr+561a 3g1YTEpxPLFMxy+iCLlF9Usc37tzAqt6JXWGAmpnAMVnfISCTFpV5nOXLXMMwA6eJd/6xZM5zR5zp nVjyCdCJgzZ4fMPieynYwBrRf+NTGMzajLF9yYvDneP3woaPf7FJ9lAXUckWlQANqyi2vlnBuTtma HB3CwHD6Tfb5uykA3hpQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hvJsQ-0003J8-EK; Wed, 07 Aug 2019 11:13:06 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hvJsL-0003If-8J for linux-arm-kernel@lists.infradead.org; Wed, 07 Aug 2019 11:13:03 +0000 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 4E3DD28; Wed, 7 Aug 2019 04:13:00 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 155FB3F575; Wed, 7 Aug 2019 04:12:58 -0700 (PDT) Date: Wed, 7 Aug 2019 12:12:57 +0100 From: Mark Rutland To: Robin Murphy Subject: Re: [PATCH] arm64: dts: allwinner: a64: Drop PMU node Message-ID: <20190807111256.GC54191@lakrids.cambridge.arm.com> References: <20190806140135.4739-1-anarsoul@gmail.com> <89402d22-d432-9551-e787-c8ede16dbe5f@arm.com> <36e60078-7dd5-9c07-ffa1-6092d8c70fa8@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <36e60078-7dd5-9c07-ffa1-6092d8c70fa8@arm.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190807_041301_575801_C6E3A52A X-CRM114-Status: GOOD ( 20.69 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: devicetree , "Jared D . McNeill" , Maxime Ripard , Chen-Yu Tsai , Rob Herring , Harald Geyer , arm-linux Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Aug 06, 2019 at 10:14:39PM +0100, Robin Murphy wrote: > On 2019-08-06 9:52 pm, Vasily Khoruzhick wrote: > > On Tue, Aug 6, 2019 at 1:19 PM Harald Geyer wrote: > > > > > > Vasily Khoruzhick writes: > > > > On Tue, Aug 6, 2019 at 7:35 AM Robin Murphy wrote: > > > > > > > > > > On 06/08/2019 15:01, Vasily Khoruzhick wrote: > > > > > > Looks like PMU in A64 is broken, it generates no interrupts at all and > > > > > > as result 'perf top' shows no events. > > > > > > > > > > Does something like 'perf stat sleep 1' at least count cycles correctly? > > > > > It could well just be that the interrupt numbers are wrong... > > > > > > > > Looks like it does, at least result looks plausible: > > > > > > I'm using perf stat regularly (cache benchmarks) and it works fine. > > > > > > Unfortunately I wasn't aware that perf stat is a poor test for > > > the interrupts part of the node, when I added it. So I'm not too > > > surprised I got it wrong. > > > > > > However, it would be unfortunate if the node got removed completely, > > > because perf stat would not work anymore. Maybe we can only remove > > > the interrupts or just fix them even if the HW doesn't work? > > > > I'm not familiar with PMU driver. Is it possible to get it working > > without interrupts? > > Yup - you get a grumpy message from the driver, it will refuse sampling > events (the ones which weren't working anyway), and if you measure anything > for long enough that a counter overflows you'll get wonky results. But for > counting hardware events over relatively short periods it'll still do the > job. Even that's stupidly dodgy; a CPU_CYCLES event could easily overflow several times between the kernel sampling it, so you can lose billions of events without any idea that happened. For other PMUs we can fix that with a hrtimer, but I think for a CPU PMU it has to be at such a high frequency that it imposes a ridiculous overhead, even assuming we can choose a sufficient frequency. :/ Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel