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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 D9B13C6786F for ; Tue, 30 Oct 2018 11:12:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AA1C520827 for ; Tue, 30 Oct 2018 11:12:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AA1C520827 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.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 S1727798AbeJ3UFc (ORCPT ); Tue, 30 Oct 2018 16:05:32 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:41646 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727381AbeJ3UFa (ORCPT ); Tue, 30 Oct 2018 16:05:30 -0400 Received: by mail-wr1-f67.google.com with SMTP id x12-v6so12100464wrw.8 for ; Tue, 30 Oct 2018 04:12:27 -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:user-agent; bh=ghItDxlpwhIE9XfKIUQsqiPKgZs52Zb1A5m2LoH9p9U=; b=X0fzieibELQsshcKTrNO9UTxEkqyPx2yTOmwqJIdjvcZszF8ZEnMQwaJSZmRPax0+n TTUaGZp1hMuGwWBUz+lwhy4R2t4xU0DWBUa3J/Y7lXSutmwi5jrJbgYY/wFNbgHxNeTw 4R4SWq/p/xxgY4kKOywctO9NI2NXE45utK0VK1UjiTR7yiS3MviPtGETiWXtlMgzAwwO Ui3q+T0PNGNDiYf0VJeSoY4qaYR+NDUG+KHjM8X5KjxxyBIZl1N1pl8fiyITdKuXVn8F qC/lywgBcWGxxA6AgU6MdzEw2949lNRQ2Ev8Odw+h+atnpedbtZRs6vELpYvNezjEMTB A/eg== X-Gm-Message-State: AGRZ1gKNROLL6pSaZBV7hygg3b+QNX7CuOTdUYRILUJ5KIEcujo7JR7e 6b44xHmJZT8P98r//WUJWc6LYw== X-Google-Smtp-Source: AJdET5esfVTbwttNY/Rkef/wgrOBGRZKzdrna/1DrX0jem5G60TcZPXqFa4vaPTaeMn2KP5K1G3jcw== X-Received: by 2002:adf:c389:: with SMTP id p9-v6mr18746731wrf.68.1540897946356; Tue, 30 Oct 2018 04:12:26 -0700 (PDT) Received: from localhost.localdomain ([151.68.156.111]) by smtp.gmail.com with ESMTPSA id p125-v6sm13749971wmp.2.2018.10.30.04.12.24 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 30 Oct 2018 04:12:25 -0700 (PDT) Date: Tue, 30 Oct 2018 12:12:21 +0100 From: Juri Lelli To: Peter Zijlstra Cc: luca abeni , Thomas Gleixner , Juri Lelli , syzbot , Borislav Petkov , "H. Peter Anvin" , LKML , mingo@redhat.com, nstange@suse.de, syzkaller-bugs@googlegroups.com, henrik@austad.us, Tommaso Cucinotta , Claudio Scordino , Daniel Bristot de Oliveira Subject: Re: INFO: rcu detected stall in do_idle Message-ID: <20181030111221.GA18091@localhost.localdomain> References: <20181016153608.GH9130@localhost.localdomain> <20181018082838.GA21611@localhost.localdomain> <20181018122331.50ed3212@luca64> <20181018104713.GC21611@localhost.localdomain> <20181018130811.61337932@luca64> <20181019113942.GH3121@hirez.programming.kicks-ass.net> <20181019225005.61707c64@nowhere> <20181024120335.GE29272@localhost.localdomain> <20181030104554.GB8177@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181030104554.GB8177@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30/10/18 11:45, Peter Zijlstra wrote: [...] > Hurm.. right. We knew of this issue back when we did it. > I suppose now it hurts and we need to figure something out. > > By virtue of being a real-time class, we do indeed need to have deadline > on the wall-clock. But if we then don't account runtime on that same > clock, but on a potentially slower clock, we get the problem that we can > run longer than our period/deadline, which is what we're running into > here I suppose. > > And yes, at some point RT workloads need to be aware of the jitter > injected by things like IRQs and such. But I believe the rationale was > that for soft real-time workloads this current semantic was 'easier' > because we get to ignore IRQ overhead for workload estimation etc. Right. In this case the task is self injecting IRQ load, but it maybe doesn't make a big difference on how we need to treat it (supposing we can actually distinguish). > What we could maybe do is track runtime in both rq_clock_task() and > rq_clock() and detect where the rq_clock based one exceeds the period > and then push out the deadline (and add runtime). > > Maybe something along such lines; does that make sense? Yeah, I think I've got the gist of the idea. I'll play with it. Thanks, - Juri