From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752245AbcAFTGO (ORCPT ); Wed, 6 Jan 2016 14:06:14 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54634 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751862AbcAFTGE (ORCPT ); Wed, 6 Jan 2016 14:06:04 -0500 Message-ID: <568D659A.3080807@redhat.com> Date: Wed, 06 Jan 2016 14:06:02 -0500 From: Prarit Bhargava User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: John Stultz , Thomas Gleixner CC: lkml , Ingo Molnar , Xunlei Pang , Peter Zijlstra , Baolin Wang , Arnd Bergmann Subject: Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() References: <1452085234-10667-1-git-send-email-prarit@redhat.com> <1452085234-10667-2-git-send-email-prarit@redhat.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/06/2016 02:04 PM, John Stultz wrote: > On Wed, Jan 6, 2016 at 9:34 AM, Thomas Gleixner wrote: >> On Wed, 6 Jan 2016, John Stultz wrote: >>> On Wed, Jan 6, 2016 at 5:00 AM, Prarit Bhargava wrote: >>>> -ktime_t ktime_get_with_offset(enum tk_offsets offs) >>>> +ktime_t ktime_get_with_offset(enum tk_offsets offs, int trylock) >>>> { >>>> struct timekeeper *tk = &tk_core.timekeeper; >>>> unsigned int seq; >>>> ktime_t base, *offset = offsets[offs]; >>>> s64 nsecs; >>>> + unsigned long flags = 0; >>>> + >>>> + if (unlikely(!timekeeping_initialized)) >>>> + return ktime_set(0, 0); >>>> >>>> WARN_ON(timekeeping_suspended); >>>> >>>> + if (trylock && !raw_spin_trylock_irqsave(&timekeeper_lock, flags)) >>>> + return ktime_set(KTIME_MAX, 0); >>> >>> Wait.. this doesn't make sense. The timekeeper lock is only for reading. >>> >>> What I was suggesting to you off line is to have something that avoids >>> spinning on the seqcounter should if a bug occurs and we IPI all the >>> cpus, that we don't deadlock or block any printk messages. >> >> We could also extend the fast timekeeper with boot/real/tai extensions and use >> that for printk. You can use ktime_get_mono_fast_ns() today. > > Ack. There'd be a chance for odd values around when the time is set, > but for debug printks I think its not critical. I'll convert to this in v2. Thanks for the input everyone! P. > > thanks > -john >