From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753939AbaDEA6Q (ORCPT ); Fri, 4 Apr 2014 20:58:16 -0400 Received: from mail-pa0-f47.google.com ([209.85.220.47]:52254 "EHLO mail-pa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752860AbaDEA6O (ORCPT ); Fri, 4 Apr 2014 20:58:14 -0400 Message-ID: <533F5524.8050500@linaro.org> Date: Fri, 04 Apr 2014 17:58:12 -0700 From: John Stultz User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Neil Zhang , akpm@linux-foundation.org CC: linux-kernel@vger.kernel.org, Lei Wen , Peter Zijlstra Subject: Re: [PATCH V2] printk: add sleep time into timestamp References: <1396322456-5195-1-git-send-email-zhangwm@marvell.com> In-Reply-To: <1396322456-5195-1-git-send-email-zhangwm@marvell.com> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/31/2014 08:20 PM, Neil Zhang wrote: > Add sleep time into timestamp to reflect the actual time since > sched_clock will be stopped during suspend. > > Thanks John Stultz for suggestion to use monotonic_to_bootbased. > > Signed-off-by: Neil Zhang > --- > kernel/printk/printk.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 4dae9cb..121f792 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -250,6 +250,18 @@ static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN); > static char *log_buf = __log_buf; > static u32 log_buf_len = __LOG_BUF_LEN; > > +static u64 print_clock(void) > +{ > + struct timespec ts; > + u64 ts_nsec = local_clock(); > + > + ts = ns_to_timespec(ts_nsec); > + monotonic_to_bootbased(&ts); > + ts_nsec = timespec_to_ns(&ts); > + Note that this is still problematic as monotonic_to_bootbased currently doesn't take the required locks to ensure it reads the data atomically. If it were fixed to take the proper locks, this would risk a deadlock since there are places where the timekeeping code takes a write on the seqlock and then may call printk (or WARN_ON). I suspect if this is going to be done, we need to have the timekeeping provide the print_clock subsystem the boottime offset when it is changed so the print_clock logic can manage this w/o grabbing timekeeping locks. But as I mentioned in reply to Lei's similar patches, I'm not a huge fan of the added complexity that will be required here when userspace like syslog can timestamps kernel messages already (so additional rational will be needed to move this forward). thanks -john