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=-3.9 required=3.0 tests=BAYES_00,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 5CD45C433E7 for ; Tue, 20 Oct 2020 11:41:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9BB42224B for ; Tue, 20 Oct 2020 11:41:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="b1oAODf2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393485AbgJTLlt (ORCPT ); Tue, 20 Oct 2020 07:41:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42248 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2393482AbgJTLlt (ORCPT ); Tue, 20 Oct 2020 07:41:49 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 68385C061755; Tue, 20 Oct 2020 04:41:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=7IzqfDrRb+pZf8s+BYZ+ICLzNkKlyZ7HBrSPDJQSEFI=; b=b1oAODf286w6odaXWhyIThR0ih 8NXQ5U9seGJlBE2Ih3XyWVekx02JKRL6vcjiu0bEVAbxihUJvaKwyRRZEMth9azKo3s/f9sg7muuX 0QArA+ATjnlQBSbUhvTwamSOcargNIQgSqYRK+goEShzyjhu7cz7bvYzVIhv7Qu+46AstP/rLYi5u INIFBv7tEdoruEcqaekU1xOYp/ijrl7y1m+8wwwZB3VApxr/b0jlJF8/34+sJyJNqoRp9clKMjnIu bI2PKhffEfLsr935flp1RQoUpUAfOv2i0hJgQQpy4wB4PvDyGMkPn8QJeJmOCqHVfEfv79XTy7zc3 KSdrepTw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kUq1K-0004bH-VA; Tue, 20 Oct 2020 11:41:40 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id B844D3011FE; Tue, 20 Oct 2020 13:41:37 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 98646203280A2; Tue, 20 Oct 2020 13:41:37 +0200 (CEST) Date: Tue, 20 Oct 2020 13:41:37 +0200 From: Peter Zijlstra To: Sebastian Andrzej Siewior Cc: Christian Eggers , tglx@linutronix.de, linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: sched: system doesn't boot since "sched: Add new migrate_disable() implementation" Message-ID: <20201020114137.GS2628@hirez.programming.kicks-ass.net> References: <1654655.1jrfHnk7pZ@n95hx1g2> <20201019150935.koqbk57dmahhomdc@linutronix.de> <20201020113009.GR2628@hirez.programming.kicks-ass.net> <20201020113828.fv7ui4h3gkrcpqoc@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20201020113828.fv7ui4h3gkrcpqoc@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Tue, Oct 20, 2020 at 01:38:28PM +0200, Sebastian Andrzej Siewior wrote: > On 2020-10-20 13:30:09 [+0200], Peter Zijlstra wrote: > > On Mon, Oct 19, 2020 at 05:09:35PM +0200, Sebastian Andrzej Siewior wrote: > > > On 2020-10-19 12:21:06 [+0200], Christian Eggers wrote: > > > > I have problems with the latest 5.9-rt releases on i.MX6ULL (!CONFIG_SMP): > > > > > > > … > > > > Any hints? > > > > > > Thank you for the report. The reason is the migrate_disable() > > > implementation for !SMP. > > > > This should fix things I suppose. I'll fold it in. > > It will. It will also break lazy-preemption. Each time a sleeping lock > is acquired there is also migrate_disable() and the migrate-disable > counter is != 0 (even for UP). The result is that a wake up for a > SCHED_OTHER task with mg counter != 0 will not lead to context switch > (same like preemption counter != 0). The difference is that a wake up > for a RT task ignores this counter and perform a context switch anyway. Right, but this patch set doesn't include the lazy preemption stuff, and given the 'fun' Valentin and me are still having with it, I'd like to keep it like that. But yes, that might warrant a slightly less NOP implementation.