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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, 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 C5B03ECE560 for ; Mon, 17 Sep 2018 11:33:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 803FF2147A for ; Mon, 17 Sep 2018 11:33:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ELqZJXDh" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 803FF2147A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org 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 S1728291AbeIQRAY (ORCPT ); Mon, 17 Sep 2018 13:00:24 -0400 Received: from merlin.infradead.org ([205.233.59.134]:36550 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726910AbeIQRAY (ORCPT ); Mon, 17 Sep 2018 13:00:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=EA6Nf0fYn1AK6GeVV3Kp3wCyzts6mhBWR/hAaZKU/rc=; b=ELqZJXDhse+pMMinsNpEDpqr7N bfoaH3WMSpJZMAWZdlzUj7NWd3MJeDJDG2zMb8/DKJfFNZb8HepLIbFkqo9KNL5FixF2UkCOeYuAa VhHddCausVn/P4eqXhzvVeCfIA7UJwyvldXr3sLFkyX2X8FePQcEw8TLV4wUc3pFATA1ivb3VtdXd yMpNMgRI8HflMORp6Fe4YUKhU28fKmrs0Tfdl1m1vkVH1p08C6AmM5fje6ne1k9OFQPnFv7KATvA8 60W8gE/yiDLa8DMMD5bPvI9AmrYnszXHzXcxgV5a9Gs3KhPxxFLwqJIsWZl/17uuPHQEB0eDNerbN dScmymJQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1g1rmI-0003Mq-I1; Mon, 17 Sep 2018 11:33:18 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id CDFEB2058A20A; Mon, 17 Sep 2018 13:33:15 +0200 (CEST) Date: Mon, 17 Sep 2018 13:33:15 +0200 From: Peter Zijlstra To: Jan =?iso-8859-1?Q?H=2E_Sch=F6nherr?= Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Paul Turner , Vincent Guittot , Morten Rasmussen , Tim Chen Subject: Re: [RFC 00/60] Coscheduling for Linux Message-ID: <20180917113315.GS24124@hirez.programming.kicks-ass.net> References: <20180907214047.26914-1-jschoenh@amazon.de> <20180914111251.GC24106@hirez.programming.kicks-ass.net> <1d86f497-9fef-0b19-50d6-d46ef1c0bffa@amazon.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1d86f497-9fef-0b19-50d6-d46ef1c0bffa@amazon.de> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 14, 2018 at 06:25:44PM +0200, Jan H. Schönherr wrote: > On 09/14/2018 01:12 PM, Peter Zijlstra wrote: > > On Fri, Sep 07, 2018 at 11:39:47PM +0200, Jan H. Schönherr wrote: > >> B) Why would I want this? > > > >> In the L1TF context, it prevents other applications from loading > >> additional data into the L1 cache, while one application tries to leak > >> data. > > > > That is the whole and only reason you did this; > It really isn't. But as your mind seems made up, I'm not going to bother > to argue. > >> 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. > > > > IOW it's completely friggin useless for L1TF. > > Do you believe me now, that L1TF is not "the whole and only reason" I did this? :D You did mention this work first to me in the context of L1TF, so I might have jumped to conclusions here. Also, I have, of course, been looking at (SMT) co-scheduling, specifically in the context of L1TF, myself. I came up with a vastly different approach. Tim - where are we on getting some of that posted? Note; that even though I wrote much of that code, I don't particularly like it either :-)