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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 5F1E5C3A5A0 for ; Mon, 19 Aug 2019 12:34:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2EF4C20851 for ; Mon, 19 Aug 2019 12:34:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566218076; bh=qUZRUg6XXT0f5v+SOKFhFDtU4L4gazRavjbpOJIOR0k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=HX4sunWUtQ7TIbIge7sRfP8f7Y5G3hby6asQXhffc2flWsUc5+t7dD51vl/bM/RGR dDhLlj8vqYf15D2+N3HD9o34t7FwGtdsF+JMgoGkDobwAvvWbA6JFFtxCjO8tgEklM oJZ/vR8PDFZqdNc4CAgfgPiQQRbhDG7XvC6kBSq4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726776AbfHSMef (ORCPT ); Mon, 19 Aug 2019 08:34:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:32916 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726594AbfHSMef (ORCPT ); Mon, 19 Aug 2019 08:34:35 -0400 Received: from localhost (lfbn-ncy-1-174-150.w83-194.abo.wanadoo.fr [83.194.254.150]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7E08320843; Mon, 19 Aug 2019 12:34:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566218075; bh=qUZRUg6XXT0f5v+SOKFhFDtU4L4gazRavjbpOJIOR0k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nBZ8qqe1kIXDaKDYQ4qvUxEOWRp6+jTytuFjbjBrYSFxAUwueXUJP+ChZBCScu7Dw /dnaL+fa88CawqqGukP3zKs22zQCrtVVPrwDyMoUtkqsGCMKOs+XxK4AcK1bsmhEmp AYBGDVQoLO6eTPV6bgqZH9rJl0TzxkGdjkPC7E7Y= Date: Mon, 19 Aug 2019 14:34:32 +0200 From: Frederic Weisbecker To: Joel Fernandes Cc: "Paul E. McKenney" , rcu@vger.kernel.org Subject: Re: need_heavy_qs flag for PREEMPT=y kernels Message-ID: <20190819123432.GB27088@lenoir> References: <20190812035306.GE28441@linux.ibm.com> <20190812212013.GB48751@google.com> <20190812230138.GS28441@linux.ibm.com> <20190813010249.GA129011@google.com> <20190815171714.GA1023@linux.ibm.com> <20190815200432.GB23194@google.com> <20190815203107.GL28441@linux.ibm.com> <20190815212216.GA224191@google.com> <20190815214542.GM28441@linux.ibm.com> <20190816000201.GC225926@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190816000201.GC225926@google.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Thu, Aug 15, 2019 at 08:02:01PM -0400, Joel Fernandes wrote: > On Thu, Aug 15, 2019 at 02:45:42PM -0700, Paul E. McKenney wrote: > > As I understand it, tick_dep_mask forces the tick on globally, > > ts->tick_dep_mask forces it on for a specific CPU (which RCU uses when it > > needs a quiescent state from that CPU), current->tick_dep_mask forces > > it on for a specific task (which RCU uses for callback invocation > > and certain rcutorture kthreads), and I don't pretend to understand > > current->signal->tick_dep_mask (the comment says something about POSIX > > CPU timers). > > Right. I am pretty new to all of these so I could have something incorrect in > a hurry. But thanks for the explanation of your understanding of these. > > Yes this commit talks about timers as well for the signal->tick_dep_mask: > d027d45d8a17 ("nohz: New tick dependency mask") FWIW, the signal->tick_dep_mask is a thread group wide tick dependency. I'm not proud of that requirement but we need to keep it for posix CPU timers that can elapse a timer on all threads of a same process and the tick is the cheapest way to account for that.