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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7A30AC33CA4 for ; Fri, 10 Jan 2020 10:35:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 503F22077C for ; Fri, 10 Jan 2020 10:35:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578652507; bh=O6NFD8wrjXHYKqN+wmpbS8vPepwh3hMeCNx2Yl2KWXE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=aeAQMfcQnQAjOUghbf6VV2A+mDT2gQh8q1AQl6vL9lxIcdTut7G6cA+bfdNHkgC7/ 2L7Sybucie6WP0eN8PZBhXHdLcGFq2a3tMhWnD2/Ur1Hjaur5Gf3dpfj24OiLrQzVa 6k8+9RBdy7dXJb1XRJe6fsrJRLIyLANDw0LBf524= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727540AbgAJKfF (ORCPT ); Fri, 10 Jan 2020 05:35:05 -0500 Received: from mail.kernel.org ([198.145.29.99]:33502 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726697AbgAJKfE (ORCPT ); Fri, 10 Jan 2020 05:35:04 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (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 388AD20721; Fri, 10 Jan 2020 10:35:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578652504; bh=O6NFD8wrjXHYKqN+wmpbS8vPepwh3hMeCNx2Yl2KWXE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=xr/aOlKnna+8ImgwYVYrX/FO51itRz4WR2ANaPtBOe7Ev2SwQbYcJxsSK3Hu4vyNj ZEJTTwb/4LBdTHTkmxMi/DH30avrAgkjBuFWaYkiuUl4AnKAcRt0Xqlv3UBKxr+8+T UvesEDS8NdT707Y/g6A9bWM7gZwjffQyYxVKKfBU= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1iprd8-0007Js-6n; Fri, 10 Jan 2020 10:35:02 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Fri, 10 Jan 2020 10:35:02 +0000 From: Marc Zyngier To: Jianyong Wu Cc: netdev@vger.kernel.org, yangbo.lu@nxp.com, john.stultz@linaro.org, tglx@linutronix.de, pbonzini@redhat.com, sean.j.christopherson@intel.com, richardcochran@gmail.com, Mark Rutland , will@kernel.org, Suzuki Poulose , Steven Price , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Steve Capper , Kaly Xin , Justin He , nd Subject: Re: [RFC PATCH v9 7/8] ptp: arm64: Enable ptp_kvm for arm64 In-Reply-To: References: <20191210034026.45229-1-jianyong.wu@arm.com> <20191210034026.45229-8-jianyong.wu@arm.com> Message-ID: X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.8 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: Jianyong.Wu@arm.com, netdev@vger.kernel.org, yangbo.lu@nxp.com, john.stultz@linaro.org, tglx@linutronix.de, pbonzini@redhat.com, sean.j.christopherson@intel.com, richardcochran@gmail.com, Mark.Rutland@arm.com, will@kernel.org, Suzuki.Poulose@arm.com, Steven.Price@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Steve.Capper@arm.com, Kaly.Xin@arm.com, Justin.He@arm.com, nd@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hi Jianyong, On 2020-01-10 10:15, Jianyong Wu wrote: > Hi Marc, [...] >> >> > + ktime_overall = hvc_res.a0 << 32 | hvc_res.a1; >> >> > + *ts = ktime_to_timespec64(ktime_overall); >> >> > + *cycle = hvc_res.a2 << 32 | hvc_res.a3; >> >> >> >> So why isn't that just a read of the virtual counter, given that what >> >> you do in the hypervisor seems to be "cntpct - cntvoff"? >> >> >> >> What am I missing here? >> >> >> > We need get clock time and counter cycle at the same time, so we can't >> > just read virtual counter at guest and must get it from host. >> >> See my comment in my reply to patch #6: *Must* seems like a very >> strong >> word, and you don't explain *why* that's better than just computing >> the >> total hypercall cost. Hint: given the frequency of the counter (in the >> few MHz >> range) vs the frequency of a CPU (in the multiple GHz range, and with >> an IPC >> close enough to 1), I doubt that you'll see the counter making much >> progress >> across a hypercall. >> > Sorry, I will avoid to use those strong words. > > It's really the case that the hypercall won't across cycle in general. > But sometimes, kernel preempt > may happen in the middle of the hypercall which we can't assume how > long before schedule back. so it's better capture them > together at the same time. Fair enough. Please document the rational, as I guess others will ask the same questions. Then the problem to solve is that of the reference counter, as you so far assume the virtual counter. I guess you need to be able to let the guest select the reference counter when calling the PTP service. [...] > By the way, does nested virtualization diff between arm64 and arm32? There is no nested virt for 32bit (it is explicitly forbidden by the architecture). M. -- Jazz is not dead. It just smells funny...