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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 AF8EFC433E0 for ; Fri, 7 Aug 2020 13:30:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CB4F20866 for ; Fri, 7 Aug 2020 13:30:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="R4iat7ri" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726226AbgHGNau (ORCPT ); Fri, 7 Aug 2020 09:30:50 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:43704 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726067AbgHGNas (ORCPT ); Fri, 7 Aug 2020 09:30:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596807047; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=JlW88KfYji9Ra9jnSteVpNm3mvfdBDzitQCHAgDFcO8=; b=R4iat7riAHVIjqYrB8eri2vPyuoClAzlMcV6FEhTBuR7hcforFolfEL1xV3s++fzFOoXrc Rn30h7orAJNpV3YU8T30uAUUzshVcsytwYTmOJQvsuGUzsYCbwL3StnMF1ymCML7de5f0j UmIGIJDFWip+LsQ3QazCOzpe5Vv7GQ8= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-258-HySBd_eTPO2mxkcQeO432w-1; Fri, 07 Aug 2020 09:30:45 -0400 X-MC-Unique: HySBd_eTPO2mxkcQeO432w-1 Received: by mail-wr1-f71.google.com with SMTP id r29so756734wrr.10 for ; Fri, 07 Aug 2020 06:30:45 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=JlW88KfYji9Ra9jnSteVpNm3mvfdBDzitQCHAgDFcO8=; b=sZx11pWT/vq4T+qsvqmgINL7d8RF9UCpSnIZ4+CCHWaqb9+0bcGTMoXkXO1Wa1ClB1 QMqsqi3V43M/BZl226faiy2Uahnn6jzi5Vordqey9czwBjB3htGU7d03NBe6vvEXsAUD h9BgBZ6cKA099BvtD7ImX02FJsacNcVYFuBjC0L31FYAvfOyjN8Ah5nPDN0qIf1Fb+um X9GpyQKcyyckBljr84fKMKmosTM4kbnRRlrOskb84/ziteQ0EcJpy5ATe+p5rDuvJMwP WbR2dL2hs3ByRjML5HhTYk9AZtZOLsdr/DX/I/FkVv8zhzw4yxDQwr/20gQTWUlmYpbr VGwg== X-Gm-Message-State: AOAM530zZm2SqgO3mYUet0tu8lITXOjI11djcc61NAET7OhGnuvRG/r6 +s/RXW8oi2F4KNaX9QgN83T3I0Cn0NxntBQjpVTdVxV9082sPV0/EEuRPmTQk+Ro6JqcKBCLR/c W6hx6NiCNsUB+RKBe3lvYgdbB X-Received: by 2002:a1c:8094:: with SMTP id b142mr13602045wmd.59.1596807044405; Fri, 07 Aug 2020 06:30:44 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwJXju9dEYjqzXP/t/6RanLHxFfCcjjybxAFY39+WPY8C/mz/r5dn5/Y/9Bqa7vbGb48GF5og== X-Received: by 2002:a1c:8094:: with SMTP id b142mr13602020wmd.59.1596807044137; Fri, 07 Aug 2020 06:30:44 -0700 (PDT) Received: from localhost.localdomain ([151.29.36.84]) by smtp.gmail.com with ESMTPSA id k1sm10561732wrw.91.2020.08.07.06.30.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Aug 2020 06:30:43 -0700 (PDT) Date: Fri, 7 Aug 2020 15:30:41 +0200 From: Juri Lelli To: luca abeni Cc: peterz@infradead.org, mingo@redhat.com, rostedt@goodmis.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, tommaso.cucinotta@santannapisa.it, alessio.balsini@gmail.com, bristot@redhat.com, dietmar.eggemann@arm.com, linux-rt-users@vger.kernel.org, mtosatti@redhat.com, williams@redhat.com, valentin.schneider@arm.com Subject: Re: [RFC PATCH v2 0/6] SCHED_DEADLINE server infrastructure Message-ID: <20200807133041.GQ42956@localhost.localdomain> References: <20200807095051.385985-1-juri.lelli@redhat.com> <20200807151632.36dc6200@nowhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200807151632.36dc6200@nowhere> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Luca, On 07/08/20 15:16, luca abeni wrote: > Hi Juri, > > thanks for sharing the v2 patchset! > > In the next days I'll have a look at it, and try some tests... Thanks! > In the meanwhile, I have some questions/comments after a first quick > look. > > If I understand well, the patchset does not apply deadline servers to > FIFO and RR tasks, right? How does this patchset interact with RT > throttling? Well, it's something like the dual of it, in that RT Throttling directly throttles RT tasks to make spare CPU cycles available to fair tasks while this patchset introduces deadline servers to schedule fair tasks, thus still reserving CPU time for those (when needed). > If I understand well, patch 6/6 does something like "use deadline > servers for SCHED_OTHER only if FIFO/RR tasks risk to starve > SCHED_OTHER tasks"... Right? That's the basic idea, yes. > I understand this is because you do not > want to delay RT tasks if they are not starving other tasks. But then, > maybe what you want is not deadline-based scheduling. Maybe a > reservation-based scheduler based on fixed priorities is what you want? > (with SCHED_DEADLINE, you could provide exact performance guarantees to > SCHED_OTHER tasks, but I suspect patch 6/6 breaks these guarantees?) I agree that we are not interested in exact guarantees in this case, but why not using something that it's already there and would give us the functionality we need (fix starvation for fair)? It would also work well in presence of "real" deadline tasks I think, in that you could account for these fair servers while performing admission control. Best, Juri