From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753187AbcERPx2 (ORCPT ); Wed, 18 May 2016 11:53:28 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:50963 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751736AbcERPx1 convert rfc822-to-8bit (ORCPT ); Wed, 18 May 2016 11:53:27 -0400 Subject: Re: [PATCH] xen: add steal_clock support on x86 To: David Vrabel , Juergen Gross , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org References: <1463573758-11441-1-git-send-email-jgross@suse.com> <573C804F.6020708@oracle.com> <573C81D1.9040309@suse.com> <573C896F.4090303@oracle.com> <573C8D4A.1000005@suse.com> <573C8E16.5040409@citrix.com> Cc: sstabellini@kernel.org From: Boris Ostrovsky Message-ID: <573C8FEA.2070407@oracle.com> Date: Wed, 18 May 2016 11:53:14 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <573C8E16.5040409@citrix.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8BIT X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/18/2016 11:45 AM, David Vrabel wrote: > On 18/05/16 16:42, Juergen Gross wrote: >> On 18/05/16 17:25, Boris Ostrovsky wrote: >>> On 05/18/2016 10:53 AM, Juergen Gross wrote: >>>> On 18/05/16 16:46, Boris Ostrovsky wrote: >>>>> On 05/18/2016 08:15 AM, Juergen Gross wrote: >>>>>> } >>>>>> >>>>>> +void __init xen_time_setup_guest(void) >>>>>> +{ >>>>>> + pv_time_ops.steal_clock = xen_steal_clock; >>>>>> + >>>>>> + static_key_slow_inc(¶virt_steal_enabled); >>>>>> + /* >>>>>> + * We can't set paravirt_steal_rq_enabled as this would require the >>>>>> + * capability to read another cpu's runstate info. >>>>>> + */ >>>>>> +} >>>>> Won't we be accounting for stolen cycles twice now --- once from >>>>> steal_account_process_tick()->steal_clock() and second time from >>>>> do_stolen_accounting()? >>>> Uuh, yes. >>>> >>>> I guess I should rip do_stolen_accounting() out, too? >>> I don't think PARAVIRT_TIME_ACCOUNTING is always selected for Xen. If >> This is easy to accomplish. :-) I looked at KVM code (PARAVIRT_TIME_ACCOUNTING is not selected there neither) and in their case that's presumably because stealing accounting is a CPUID bit, i.e. it might not be supported. In Xen case we always have this interface. >> >>> that's indeed the case then we should ifndef do_stolen_accounting(). Or >>> maybe check for paravirt_steal_enabled. >> Is this really a sensible thing to do? There is a mechanism used by KVM >> to do the stolen accounting. I think we should use it instead of having >> a second implementation doing the same thing in case the generic one >> isn't enabled. > I agree. > > Although I don't think selecting PARAVIRT_TIME_ACC' is necessary -- I > don't think it's essential (or is it?). Looks like it's useful only if paravirt_steal_rq_enabled, which we don't support yet. -boris