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,URIBL_BLOCKED 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 A9ED7C43461 for ; Thu, 17 Sep 2020 19:17:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 44F6D20874 for ; Thu, 17 Sep 2020 19:17:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="T9xqcvop" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726338AbgIQTRn (ORCPT ); Thu, 17 Sep 2020 15:17:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47828 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728396AbgIQQSX (ORCPT ); Thu, 17 Sep 2020 12:18:23 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6AB5EC061355 for ; Thu, 17 Sep 2020 08:54:28 -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-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=hSnz+23COfeSjN/62Urx3BsW/vPBbP67EbWGZophf4Q=; b=T9xqcvop0dh6dHsCjx6U+kG4ou I9s7n6jedGM1kL+raItlgC1+HPwi/EvQUdGMwSaeLSuFZHpBk1jPZyQRd6VfyE99TakP+e1Nc+kTv b0yquF5xdTs27TcfNfYvym4EBsxAPpMZxposa9XJKci2rvkRkkaYx3vYFWrZZd4fr0dWxBp25OouG ygrpHasuF+pJI7bLfHdx3rZDw6yb0rD4O1mx5GabWH8eg8pFGUTbGrfglz6+AtFISW5ZQJD2A2F0B jmVoXRewoGl+lTXXjTJEfPL/3RO8KF1LrW9XecB7le6URosk48vmRD9BmvXZbJSStUUlx1nP7aPO8 Vp2VuY2Q==; 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 1kIwEf-0004Aw-JP; Thu, 17 Sep 2020 15:54:13 +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 973EF3019CE; Thu, 17 Sep 2020 17:54:10 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 79D222BCBFCFC; Thu, 17 Sep 2020 17:54:10 +0200 (CEST) Date: Thu, 17 Sep 2020 17:54:10 +0200 From: peterz@infradead.org To: Sebastian Siewior Cc: Thomas Gleixner , LKML , Qais Yousef , Scott Wood , Valentin Schneider , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Vincent Donnefort Subject: Re: [patch 09/10] sched/core: Add migrate_disable/enable() Message-ID: <20200917155410.GK1362448@hirez.programming.kicks-ass.net> References: <20200917094202.301694311@linutronix.de> <20200917101624.813835219@linutronix.de> <20200917142438.GH1362448@hirez.programming.kicks-ass.net> <20200917143850.25akkvr32ojtwohy@linutronix.de> <20200917144937.GI1362448@hirez.programming.kicks-ass.net> <20200917151341.2ilqamtnc6hperix@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200917151341.2ilqamtnc6hperix@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 17, 2020 at 05:13:41PM +0200, Sebastian Siewior wrote: > On 2020-09-17 16:49:37 [+0200], peterz@infradead.org wrote: > > I'm aware of the duct-tape :-) But I was under the impression that we > > didn't want the duct-tape, and that there was lots of issues with the > > FPU code, or was that another issue? > > Of course it would be better not to need the duct tape. > Also symmetrical locking is what you want but clearly futex is one of > a kind. > > I'm currently not aware of any issues in the FPU code in regard to this. > A few weeks ago, I was looking for this kind of usage and only futex > popped up. I'm not sure what the problem with FPU was, I was throwing alternatives at tglx to see what would stick, in part to (re)discover the design constraints of this thing. One reason for not allowing migrate_disable() to sleep was: FPU code. Could it be it does something like: preempt_disable(); spin_lock(); spin_unlock(); preempt_enable(); Where we'll never get preempted while migrate_disable()'d and thus never trigger any of the sleep paths?