From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751820AbeEDRiK (ORCPT ); Fri, 4 May 2018 13:38:10 -0400 Received: from aserp2130.oracle.com ([141.146.126.79]:49544 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751423AbeEDRiJ (ORCPT ); Fri, 4 May 2018 13:38:09 -0400 Subject: Re: [RFC] sched/core: Don't schedule threads on pre-empted vcpus To: Steven Sistare Cc: Peter Zijlstra , matt@codeblueprint.co.uk, mingo@kernel.org, dhaval.giani@oracle.com, subhra.mazumdar@oracle.com, linux-kernel@vger.kernel.org References: <1525294330-7759-1-git-send-email-rohit.k.jain@oracle.com> <20180504094716.GL12217@hirez.programming.kicks-ass.net> <19c761ee-0865-cc32-1728-0c3ccaf5814a@oracle.com> <0a1b4e9d-691c-29bb-37f9-43b62aa8234c@oracle.com> From: Rohit Jain Message-ID: <49135b7a-28d2-682d-77de-b94862f11dc1@oracle.com> Date: Fri, 4 May 2018 10:37:48 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <0a1b4e9d-691c-29bb-37f9-43b62aa8234c@oracle.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8883 signatures=668698 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1805040161 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steve, On 05/04/2018 10:32 AM, Steven Sistare wrote: > On 5/4/2018 1:22 PM, Rohit Jain wrote: >> Hi Peter, >> >> On 05/04/2018 02:47 AM, Peter Zijlstra wrote: >>> On Wed, May 02, 2018 at 01:52:10PM -0700, Rohit Jain wrote: >>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >>>> index 5e10aae..75d1ecf 100644 >>>> --- a/kernel/sched/core.c >>>> +++ b/kernel/sched/core.c >>>> @@ -4033,6 +4033,9 @@ int idle_cpu(int cpu) >>>>           return 0; >>>>   #endif >>>>   +    if (vcpu_is_preempted(cpu)) >>>> +        return 0; >>>> + >>>>       return 1; >>>>   } >>> Basically OK with this, but did you consider idle_cpu() usage outside of >>> select_idle_sibling()? >>> >>> For instance, I think got_nohz_idle_kick() isn't quite right with this >>> on. Similarly for scheduler_tick(), that wants the actual idle state. >> As far as intent is concerned, yes I agree you might be right. I left >> the VM running for a couple of days, didn't see anything weird however. >> >> We could add a check at each of those places or something to that effect >> if this is an issue. Please let me know how you want to proceed. > The point is that some idle_cpu() call sites should consider preemption state > and some should not, and they must be considered on a case by case basis. You > could define a new accessor to abstract the difference, and call it from > select_idle_sibling and anywhere else it makes sense. > > available_idle_cpu() > { > return idle_cpu() && !vcpu_is_preempted() > } Great! That's what I was thinking as "something to that effect" :) Thanks, Rohit