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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 61573C0044C for ; Thu, 1 Nov 2018 03:23:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 16C8620821 for ; Thu, 1 Nov 2018 03:23:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 16C8620821 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.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 S1727634AbeKAMYP (ORCPT ); Thu, 1 Nov 2018 08:24:15 -0400 Received: from mga04.intel.com ([192.55.52.120]:28693 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726327AbeKAMYO (ORCPT ); Thu, 1 Nov 2018 08:24:14 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 31 Oct 2018 20:23:09 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,450,1534834800"; d="scan'208";a="83156716" Received: from yisun1-ubuntu.bj.intel.com (HELO localhost) ([10.238.156.104]) by fmsmga008.fm.intel.com with ESMTP; 31 Oct 2018 20:23:07 -0700 Date: Thu, 1 Nov 2018 11:20:21 +0800 From: Yi Sun To: Peter Zijlstra Cc: Waiman Long , Juergen Gross , 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 Subject: Re: [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall Message-ID: <20181101032020.GE15378@yi.y.sun> References: <2e0d62cb-b706-a5b4-65f7-982a913fb32b@suse.com> <20181022171516.GH3117@worktop.programming.kicks-ass.net> <20181023025740.GL11769@yi.y.sun> <20181023085127.GG3109@worktop.c.hoisthospitality.com> <20181023093328.GA15378@yi.y.sun> <20181031015417.GC15378@yi.y.sun> <20181031141030.GB13219@hirez.programming.kicks-ass.net> <20181031171538.GC13219@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181031171538.GC13219@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18-10-31 18:15:39, Peter Zijlstra wrote: > On Wed, Oct 31, 2018 at 11:07:22AM -0400, Waiman Long wrote: > > On 10/31/2018 10:10 AM, Peter Zijlstra wrote: > > > On Wed, Oct 31, 2018 at 09:54:17AM +0800, Yi Sun wrote: > > >> On 18-10-23 17:33:28, Yi Sun wrote: > > >>> On 18-10-23 10:51:27, Peter Zijlstra wrote: > > >>>> Can you try and explain why vcpu_is_preempted() doesn't work for you? > > >>> I thought HvSpinWaitInfo is used to notify hypervisor the spin number > > >>> which is different with vcpu_is_preempted. So I did not consider > > >>> vcpu_is_preempted. > > >>> > > >>> But HvSpinWaitInfo is a quite simple function and could be combined > > >>> with vcpu_is_preempted together. So I think it is OK to use > > >>> vcpu_is_preempted to make codes clean. I will have a try. > > >> After checking codes, there is one issue to call vcpu_is_preempted. > > >> There are two spin loops in qspinlock_paravirt.h. One loop in > > >> 'pv_wait_node' calls vcpu_is_preempted. But another loop in > > >> 'pv_wait_head_or_lock' does not call vcpu_is_preempted. It also does > > >> not call any other ops of 'pv_lock_ops' in the loop. So I am afraid > > >> we have to add one more ops in 'pv_lock_ops' to do this. > > > Why? Would not something like the below cure that? Waiman, can you have > > > a look at this; I always forget how that paravirt crud works. > > > > There are two major reasons why the vcpu_is_preempt() test isn't done at > > pv_wait_head_or_lock(). First of all, we may not have a valid prev > > pointer after all if it is the first one to enter the queue while the > > lock is busy. Secondly, because of lock stealing, the cpu number pointed > > by a valid prev pointer may not be the actual cpu that is currently > > holding the lock. Another minor reason is that we want to minimize the > > lock transfer latency and so don't want to sleep too early while waiting > > at the queue head. > > So Yi, are you actually seeing a problem? If so, can you give details? Where does the patch come from? I cannot find it through google. Per Waiman's comment, it seems not suitable to call vcpu_is_preempted() in pv_wait_head_or_lock(). So, we cannot make HvSpinWaitInfo notification through vcpu_is_preempted() for such case. Based on that, I suggest to add one more callback function in pv_lock_ops. BTW, which performance test do you suggest? I am trying to test it by AIM7.