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 F2C39C433DF for ; Fri, 7 Aug 2020 14:11:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CC4BB22CA1 for ; Fri, 7 Aug 2020 14:11:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RBd3rcPF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726233AbgHGOLx (ORCPT ); Fri, 7 Aug 2020 10:11:53 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:37100 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725893AbgHGOLm (ORCPT ); Fri, 7 Aug 2020 10:11:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596809501; 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=3c1yw7k9X8hm0dHhBiwxK4zbTgM0Mhf/wXgVInw3T7o=; b=RBd3rcPFwHz/eJQ2LlX+tnHbg3xoi2tmGJ4MBmR/ZwCqz5H7dzNYEvK0Wfelh7KlvdGCfD 44Ve8WPX3yv4+KQ+pDZYT5HvI5QpGwTqbhtRKsZLk2bDNv2a/Rj5NrdR/slZka6V36K/mC kymkjOTafw+ZNS4J7sQZfK7cUM0GFtM= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-18-cFoMWULnP-y8Y_3D1LSeEw-1; Fri, 07 Aug 2020 10:11:39 -0400 X-MC-Unique: cFoMWULnP-y8Y_3D1LSeEw-1 Received: by mail-wr1-f69.google.com with SMTP id k11so798248wrv.1 for ; Fri, 07 Aug 2020 07:11:39 -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=3c1yw7k9X8hm0dHhBiwxK4zbTgM0Mhf/wXgVInw3T7o=; b=OS5vtyyk+TzJYeObt58wcZXp2RiZGZgyWhtnk/bpZ2qDSytJZ4dXnkoeWXrzbC9Vic +tDHD5/Q45s85FI48PVE4HKgrEX9j9ynPVYEiBvs9gBkrCZdPAFyg4eAyJ7pV002DD4Q C9KgZbgPRX0pXfCb+mtYoqlaSum9wjfOXdj3ItRTuZZCTKDp+wCJnRU6VsWOFaTgQGdr 46EoduGzjVME6kmIZGNTwI2UsYwNVPuuqkCvDVCElEfu8vYBx9KZiB5BOKyPBw6lwlwB XyHbkVLgZnny6ru9CjduLT9hdX2maPpSZTK5knt0Nzaxq9IL2EhAdQLd6f7nnMesLL95 BsEw== X-Gm-Message-State: AOAM533nxM2XxtJCnuOPeUCkk1Iby8vLh4iZOJVJSBcYohq7h5Yq8q4R JWQxbzuibkkJ1pXax3yFbUntROK1EAZWIICRcT/MEaTQ4j+gNkV/O7HrRAc2gUReifZVGfxRq9K yh6wulqTZrnDWU/Z4lJ9U+DKBq9Y= X-Received: by 2002:adf:81c5:: with SMTP id 63mr12748567wra.185.1596809498218; Fri, 07 Aug 2020 07:11:38 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzvEkand5vtybeLw6SUi+cwMVVl7XbxNslOqTgZI0RMJgnMHG9r2j1ZQJPEaSceKtI6AHDGog== X-Received: by 2002:adf:81c5:: with SMTP id 63mr12748548wra.185.1596809497939; Fri, 07 Aug 2020 07:11:37 -0700 (PDT) Received: from localhost.localdomain ([151.29.36.84]) by smtp.gmail.com with ESMTPSA id o124sm10775755wmb.2.2020.08.07.07.11.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Aug 2020 07:11:37 -0700 (PDT) Date: Fri, 7 Aug 2020 16:11:35 +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 6/6] sched/fair: Implement starvation monitor Message-ID: <20200807141135.GT42956@localhost.localdomain> References: <20200807095051.385985-1-juri.lelli@redhat.com> <20200807095604.GO42956@localhost.localdomain> <20200807152832.591f462e@nowhere> <20200807134353.GR42956@localhost.localdomain> <20200807155510.2b380f49@nowhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200807155510.2b380f49@nowhere> Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On 07/08/20 15:55, luca abeni wrote: > On Fri, 7 Aug 2020 15:43:53 +0200 > Juri Lelli wrote: > > > On 07/08/20 15:28, luca abeni wrote: > > > Hi Juri, > > > > > > On Fri, 7 Aug 2020 11:56:04 +0200 > > > Juri Lelli wrote: > > > > > > > Starting deadline server for lower priority classes right away > > > > when first task is enqueued might break guarantees > > > > > > Which guarantees are you thinking about, here? Response times of > > > fixed priority tasks? > > > > Response time, but also wakeup latency (which, for better or worse, is > > another important metric). > > > > > If fixed priority tasks are also scheduled through deadline servers, > > > then you can provide response-time guarantees to them even when > > > lower-priority/non-real-time tasks are scheduled through deadline > > > servers. > > > > Right, but I fear we won't be able to keep current behavior for > > wakeups: RT with highest prio always gets scheduled right away? > > Uhm... I think this depends on how the servers' parameters are > designed: assigning "wrong" (or "bad") parameters to the server used to > schedule RT tasks, this property is broken. > > (however, notice that even with the current patchset the highest > priority task might be scheduled with some delay --- if the SCHED_OTHER > deadline server is active because SCHED_OTHER tasks are being starved). But that's OK I think, because if the server is active it means that OTHER didn't get a chance to run for some time and if it continues to hung than worse problems than breaking FIFO assumptions will happen. :-/