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=-2.2 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_MUTT autolearn=ham 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 BED13C43613 for ; Thu, 20 Jun 2019 16:52:35 +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 8C67020673 for ; Thu, 20 Jun 2019 16:52:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="WWk0276d" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C67020673 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=wkrQYuSW1xLCI75Db0AKLx2139GbaUpAl5OE/MizKIE=; b=WWk0276dd7S+WG Oo3XAY2lTcVIl8FD+6sboChOoJOvwTxcLiDxkkOQ2iHhj1rkk0igUUcIpQ10MDPRayV/opRajOj54 +0tJ7i5SrP6ZCCAwAyEHfYuUAA1nm2VLMdQfGg2cUZX0sdb+4JpEFsIojwmzAOv3F/FaMT5lqcRDb 4kAZbPdOnm7a74uJ3K2h+gAePjBIp3UXy8pakwM4L7QpH6mUXwDm1/qD4lDsppy7kN6hnfwA+AJoh a3rWWbvr66oGiJY9fQCl2XnJ3UqqoAbHNvYvnGm8x+fRKz9DsAezKUvmIFwZEbv6Xlz6pzixaMt+j G/IudzjMa3+Tq4lhFZ/g==; 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 1he0IX-0003Ot-SM; Thu, 20 Jun 2019 16:52:29 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1he0IV-0003OE-4s for linux-arm-kernel@lists.infradead.org; Thu, 20 Jun 2019 16:52:28 +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 555642B; Thu, 20 Jun 2019 09:52:21 -0700 (PDT) Received: from e107155-lin (e107155-lin.cambridge.arm.com [10.1.196.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 36F003F246; Thu, 20 Jun 2019 09:52:20 -0700 (PDT) Date: Thu, 20 Jun 2019 17:52:18 +0100 From: Sudeep Holla To: Mathieu Poirier Subject: Re: [PATCH v1 5/5] coresight: etm4x: save/restore state across CPU low power states Message-ID: <20190620165218.GE25273@e107155-lin> References: <20190618125433.9739-6-andrew.murray@arm.com> <20190618132159.GA18121@e107155-lin> <15ef45d4-ee1a-3c45-878d-f08f0a84cfeb@arm.com> <20190619110749.GD1360@e107155-lin> <20190620114116.GE20984@e119886-lin.cambridge.arm.com> <20190620154154.GB25273@e107155-lin> <20190620163426.GC25273@e107155-lin> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190620_095227_280065_4176B50F X-CRM114-Status: GOOD ( 23.65 ) 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: Al Grant , Suzuki K Poulose , Alexander Shishkin , Sudeep Holla , Andrew Murray , linux-arm-kernel , Mike Leach 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 Thu, Jun 20, 2019 at 10:47:38AM -0600, Mathieu Poirier wrote: > On Thu, 20 Jun 2019 at 10:34, Sudeep Holla wrote: > > > > On Thu, Jun 20, 2019 at 10:14:04AM -0600, Mathieu Poirier wrote: > > > On Thu, 20 Jun 2019 at 09:41, Sudeep Holla wrote: > > > > > > > > [...] > > > > > > Sorry but even then I prefer it not to be default and force extra work > > > > to the people who add support and constantly be reminded that it's > > > > broken and they are deviating from default behaviour in the kernel > > > > which may come and latency penalty. > > > > > > > > Making it default may hide the problem if Linux is used for some validation. > > > > > > > > Also we hardly have 3-4 platforms in upstream that support coresight, > > > > and many are broken except Juno. But that doesn't imply all others > > > > are broken and we just can't derive that unless we have more information. > > > > > > For now we have a clear trend. To me it is not a matter of broken vs. > > > non-broken but more about what people want to do or can > > > (realistically) do. > > > > > > > No disagreement there. > > > > > The coresight specification is broad and very permissive in terms of > > > implementation defined choices. It is not because the TRCPDCR.PU it > > > not taken into account by a platform that it is automatically broken. > > > This could be a design choice or a trade off. We already have two > > > ways of putting a CPU to sleep (architected or OS driven), we simply > > > do the same here for coresight. > > > > > > > Sure, if the term "broken" is inappropriate I am fine if anything else > > is used. The point is we are adding an idle notifier that adds latency > > and must be done if and only if necessary. > > > > How you identify that and implement doesn't bother me much, making > > that default just based on the fact that more platforms need it > > compared to others definitely does. So I am fine if this needs to be > > advertised *not broken* but *by design*, sure go for it. > > > > Then all we have to do is make the ACPI/DT property that indicate the > method used to deal with tracer idling mandatory. That way people are > conscious of the choice they are making. To be backward compatible > with current systems we default to the TRCPDCR.PU method but print a > warning message, just like we do for obsolete DT bindings. > If you are happy with kernel module/command line parameters, I am fine by that too. I missed that earlier, sorry for the noise. But I still need to keep the default disabled and platforms needing it must enable it. If not architectural argument, I am still concerned with latency :) -- Regards, Sudeep _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel