From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753549AbcERPyS (ORCPT ); Wed, 18 May 2016 11:54:18 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:5815 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752818AbcERPyR (ORCPT ); Wed, 18 May 2016 11:54:17 -0400 X-IronPort-AV: E=Sophos;i="5.26,329,1459814400"; d="scan'208";a="361832633" Subject: Re: [PATCH] xen: add steal_clock support on x86 To: Juergen Gross , Boris Ostrovsky , , 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> <573C8F7B.2040201@suse.com> CC: From: David Vrabel Message-ID: <573C8FCB.2000902@citrix.com> Date: Wed, 18 May 2016 16:52:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.5.0 MIME-Version: 1.0 In-Reply-To: <573C8F7B.2040201@suse.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18/05/16 16:51, Juergen Gross wrote: > On 18/05/16 17:45, 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. :-) >>> >>>> 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?). > > Not doing so will change behavior in case I rip out > do_stolen_accounting(). What about "default y if XEN" ? Ok. David