From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751908Ab3FYWQX (ORCPT ); Tue, 25 Jun 2013 18:16:23 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:51741 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751101Ab3FYWQW (ORCPT ); Tue, 25 Jun 2013 18:16:22 -0400 Date: Tue, 25 Jun 2013 15:01:52 -0700 From: "Paul E. McKenney" To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu Subject: Re: [PATCH RFC nohz_full 0/8] Provide infrastructure for full-system idle Message-ID: <20130625220152.GH3828@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20130625213721.GA19452@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13062522-4834-0000-0000-000008679212 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 25, 2013 at 11:49:47PM +0200, Thomas Gleixner wrote: > On Tue, 25 Jun 2013, Paul E. McKenney wrote: > > Note that this version pays attention to CPUs that have taken an NMI > > from idle. It is not clear to me that NMI handlers can safely access > > the time on a system that is long-term idle. Unless someone tells me > > that it is somehow safe to access time from an NMI from idle, I will > > remove NMI support in the next version. > > NMI cannot access any time related functions independent of NOHZ, long > term idle or whatever you come up with: > > write_seqcount_begin(&timekeeper_seq); > > ---> NMI > ... > do { > seq = read_seqcount_begin(&timekeeper_seq); > } while (read_seqcount_retry(&timekeeper_seq, seq)); > > Guess how well that works .... Woo-hoo!!! I will yank the NMI support on the next version. Thank you for the info! Thanx, Paul