From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id D3255721 for ; Mon, 12 Oct 2015 20:40:00 +0000 (UTC) Received: from e32.co.us.ibm.com (e32.co.us.ibm.com [32.97.110.150]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 221D2117 for ; Mon, 12 Oct 2015 20:40:00 +0000 (UTC) Received: from localhost by e32.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 12 Oct 2015 14:39:59 -0600 Received: from b03cxnp08028.gho.boulder.ibm.com (b03cxnp08028.gho.boulder.ibm.com [9.17.130.20]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 1E3C51FF004C for ; Mon, 12 Oct 2015 14:28:10 -0600 (MDT) Received: from d03av05.boulder.ibm.com (d03av05.boulder.ibm.com [9.17.195.85]) by b03cxnp08028.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t9CKcfF612321258 for ; Mon, 12 Oct 2015 13:38:41 -0700 Received: from d03av05.boulder.ibm.com (localhost [127.0.0.1]) by d03av05.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t9CKduv9016038 for ; Mon, 12 Oct 2015 14:39:57 -0600 Date: Mon, 12 Oct 2015 13:40:05 -0700 From: "Paul E. McKenney" To: "Theodore Ts'o" , Andy Lutomirski , "ksummit-discuss@lists.linuxfoundation.org" , "linux-kernel@vger.kernel.org" , Christoph Lameter , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Peter Zijlstra , Chris Metcalf , Rik van Riel Message-ID: <20151012204005.GI3910@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20151012184051.GB29127@thunk.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151012184051.GB29127@thunk.org> Subject: Re: [Ksummit-discuss] [BELATED CORE TOPIC] context tracking / nohz / RCU state List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Oct 12, 2015 at 02:40:51PM -0400, Theodore Ts'o wrote: > This thread had fairly intense discussion for two days, but then went dead. > > Do folks think this is worth discussing at the kernel summit? I am very interested in discussing this. Of course, part of that interest is due to the direct involvement of RCU code. Thanx, Paul > thanks, > > - Ted > > > > On Tue, Aug 11, 2015 at 10:49:36AM -0700, Andy Lutomirski wrote: > > This is a bit late, but here goes anyway. > > > > Having played with the x86 context tracking hooks for awhile, I think > > it would be nice if core code that needs to be aware of CPU context > > (kernel, user, idle, guest, etc) could come up with single, > > comprehensible, easily validated set of hooks that arch code is > > supposed to call. > > > > Currently we have: > > > > - RCU hooks, which come in a wide variety to notify about IRQs, NMIs, etc. > > > > - Context tracking hooks. Only used by some arches. Calling these > > calls the RCU hooks for you in most cases. They have weird > > interactions with interrupts and they're slow. > > > > - vtime. Beats the heck out of me. > > > > - Whatever deferred things Christoph keeps reminding us about. > > > > Honestly, I don't fully understand what all these hooks are supposed > > to do, nor do I care all that much. From my perspective, the code > > code should be able to do whatever it wants and rely on appropriate > > notifications from arch code. It would be great if we could come up > > with something straightforward that covers everything. For example: > > > > user_mode_to_kernel_mode() > > kernel_mode_to_user_mode() > > kernel_mode_to_guest_mode() > > in_a_periodic_tick() > > starting_nmi() > > ending_nmi() > > may_i_turn_off_ticks_right_now() > > or, better yet: > > i_am_turning_off_ticks_right_now_and_register_your_own_darned_hrtimer_if_thats_a_problem() > > > > Some arches may need: > > > > i_am_lame_and_forgot_my_previous_context() > > > > x86 will soon (4.3 or 4.4, depending on how my syscall cleanup goes) > > no longer need that. > > > > Paul says that some arches need something that goes straight from IRQ > > to user mode (?) -- sigh. > > > > etc. > > > > It might make sense to get enough people who understand what's going > > on behind the scenes together to hash out the requirements. > > > > --Andy > > _______________________________________________ > > Ksummit-discuss mailing list > > Ksummit-discuss@lists.linuxfoundation.org > > https://lists.linuxfoundation.org/mailman/listinfo/ksummit-discuss >