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=-1.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 3D31CECDE46 for ; Fri, 26 Oct 2018 23:06:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C38852085B for ; Fri, 26 Oct 2018 23:06:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="U31uksvd" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C38852085B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=oracle.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 S1728301AbeJ0HpS (ORCPT ); Sat, 27 Oct 2018 03:45:18 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:57518 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727514AbeJ0HpS (ORCPT ); Sat, 27 Oct 2018 03:45:18 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.22/8.16.0.22) with SMTP id w9QN4ICE116328; Fri, 26 Oct 2018 23:05:55 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=E2TBzyRn4FlZDssLAOxZ1HbDJPookG1+ECYnRV9id/A=; b=U31uksvdoYOnWiyTkL18NMEqLO/sUBppiU8JaG09naPwnKkM6s+0PAcPPoxehdUpcxs3 Ghg1BoIsVwgW2DJ6eSc/PqwwQO1Tz1j1NweSjDOa5gojiRT4ZoGMSOE8TCXF6VTD46P5 2UVoTRsiXsnQ0x1A3cUU6cZ1SImEEwDVHK6Em4eA2Q/hi7J5Ya6j1lrWJco0S5Mrkg81 4VoG7NyJbJ8pY9OGu9jk7qCcTFtynkGhcLRMs6We18kgaAxHV+53EQyEZ0wb4ByCEcqt +cszmW8889HReK7+1Y2DWfRq67IckUikU7XtSVCHTh7SDFgWA8f9aGd7JNQK6XprTTzu bw== Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by userp2130.oracle.com with ESMTP id 2n7ususj03-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 26 Oct 2018 23:05:54 +0000 Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id w9QN5sKL005016 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 26 Oct 2018 23:05:54 GMT Received: from abhmp0013.oracle.com (abhmp0013.oracle.com [141.146.116.19]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id w9QN5rkp008015; Fri, 26 Oct 2018 23:05:54 GMT Received: from [10.132.91.175] (/10.132.91.175) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 26 Oct 2018 16:05:52 -0700 Subject: Re: [RFC 00/60] Coscheduling for Linux To: =?UTF-8?Q?Jan_H=2e_Sch=c3=b6nherr?= , Ingo Molnar , Peter Zijlstra Cc: linux-kernel@vger.kernel.org References: <20180907214047.26914-1-jschoenh@amazon.de> From: Subhra Mazumdar Message-ID: <65abfba5-7c51-fd99-898e-f6e74969fea3@oracle.com> Date: Fri, 26 Oct 2018 16:05:10 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20180907214047.26914-1-jschoenh@amazon.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9058 signatures=668683 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=8.0.1-1807170000 definitions=main-1810260192 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > D) What can I *not* do with this? > --------------------------------- > > Besides the missing load-balancing within coscheduled task-groups, this > implementation has the following properties, which might be considered > short-comings. > > This particular implementation focuses on SCHED_OTHER tasks managed by CFS > and allows coscheduling them. Interrupts as well as tasks in higher > scheduling classes are currently out-of-scope: they are assumed to be > negligible interruptions as far as coscheduling is concerned and they do > *not* cause a preemption of a whole group. This implementation could be > extended to cover higher scheduling classes. Interrupts, however, are an > orthogonal issue. > > The collective context switch from one coscheduled set of tasks to another > -- while fast -- is not atomic. If a use-case needs the absolute guarantee > that all tasks of the previous set have stopped executing before any task > of the next set starts executing, an additional hand-shake/barrier needs to > be added. > The leader doesn't kick the other cpus _immediately_ to switch to a different cosched group. So threads from previous cosched group will keep running in other HTs till their sched_slice is over (in worst case). This can still keep the window of L1TF vulnerability open?