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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS 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 4659DC004D3 for ; Mon, 22 Oct 2018 17:27:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E466920645 for ; Mon, 22 Oct 2018 17:27:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E466920645 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728851AbeJWBq4 convert rfc822-to-8bit (ORCPT ); Mon, 22 Oct 2018 21:46:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47172 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728658AbeJWBqz (ORCPT ); Mon, 22 Oct 2018 21:46:55 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 924438830E; Mon, 22 Oct 2018 17:27:31 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-8.bos.redhat.com [10.18.17.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id 28D2E60BF7; Mon, 22 Oct 2018 17:27:28 +0000 (UTC) Subject: Re: [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall To: Peter Zijlstra Cc: Juergen Gross , Yi Sun , linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de, chao.p.peng@intel.com, chao.gao@intel.com, isaku.yamahata@intel.com, michael.h.kelley@microsoft.com, tianyu.lan@microsoft.com, "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , "mingo@redhat.com" , Will Deacon References: <1539954835-34035-1-git-send-email-yi.y.sun@linux.intel.com> <1539954835-34035-3-git-send-email-yi.y.sun@linux.intel.com> <20181022015342.GK11769@yi.y.sun> <2e0d62cb-b706-a5b4-65f7-982a913fb32b@suse.com> <20181022171516.GH3117@worktop.programming.kicks-ass.net> From: Waiman Long Organization: Red Hat Message-ID: <6d8095c0-af95-5967-3ca5-2ceeb74233ea@redhat.com> Date: Mon, 22 Oct 2018 13:27:27 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20181022171516.GH3117@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Mon, 22 Oct 2018 17:27:31 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/22/2018 01:15 PM, Peter Zijlstra wrote: > Firstly, who come a patch that is grubbing around in kernel/locking/ has > an x86/hyperv subject and isn't Cc'ed to the locking maintainers? > > On Mon, Oct 22, 2018 at 12:31:45PM -0400, Waiman Long wrote: >> On 10/22/2018 03:32 AM, Juergen Gross wrote: >>> On 22/10/2018 03:53, Yi Sun wrote: >>>> On 18-10-19 16:20:52, Juergen Gross wrote: >>>>> On 19/10/2018 15:13, Yi Sun wrote: >>>> [...] >>>> >>>>>> diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h >>>>>> index 0130e48..9e88c7e 100644 >>>>>> --- a/kernel/locking/qspinlock_paravirt.h >>>>>> +++ b/kernel/locking/qspinlock_paravirt.h >>>>>> @@ -7,6 +7,8 @@ >>>>>> #include >>>>>> #include >>>>>> >>>>>> +#include >>>>>> + >>>>>> /* >>>>>> * Implement paravirt qspinlocks; the general idea is to halt the vcpus instead >>>>>> * of spinning them. >>>>>> @@ -305,6 +307,10 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev) >>>>>> wait_early = true; >>>>>> break; >>>>>> } >>>>>> +#if defined(CONFIG_X86_64) && defined(CONFIG_PARAVIRT_SPINLOCKS) && IS_ENABLED(CONFIG_HYPERV) >>>>>> + if (!hv_notify_long_spin_wait(SPIN_THRESHOLD - loop)) >>>>>> + break; >>>>>> +#endif > Secondly; how come you thought that was acceptable in any way shape or > form? > >>> vcpu_is_preempted() is already part of this loop. And this is a paravirt >>> hook. Can't you make use of that? This might require adding another >>> parameter to this hook, but I'd prefer that over another pv-spinlock >>> hook. >> I agree with Juergen on that. I would suggest rename the >> vcpu_is_preempted hook into a more generic vcpu_stop_spinning, perhaps, >> so different hypervisors can act on the information accordingly. Adding >> an extra parameter is fine. > No; no extra parameters. vcpu_is_preempted() is a simple and intuitive > interface. Why would we want to make it complicated? Hyperv seems to do it in a somewhat different way by looking at the spin counter and decide if it should continue. I don't know why they do that and what advantage it has. The current patch is definitely not OK. A revised patch that makes use of an existing paravirt hook will be more acceptable. Again, I would like to see some performance figure and why they do it this way to see if it is worthwhile to change the existing interface. Cheers, Longman