linux-kernel - Re: [PATCH] printk, allow different timestamps for printk.time

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Date:	Wed, 27 Jan 2016 10:39:17 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Prarit Bhargava <prarit@...hat.com>
cc:	linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
	Xunlei Pang <pang.xunlei@...aro.org>,
	Baolin Wang <baolin.wang@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Petr Mladek <pmladek@...e.cz>, Tejun Heo <tj@...nel.org>,
	Peter Hurley <peter@...leysoftware.com>,
	Vasily Averin <vvs@...tuozzo.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH] printk, allow different timestamps for printk.time

On Tue, 26 Jan 2016, Prarit Bhargava wrote:
> On 01/26/2016 03:34 PM, Thomas Gleixner wrote:
> > Just for the record: The fast timekeeper stops across the inner workings of
> > suspend/resume. But I think that doesn't matter much.
> 
> I've had to debug s/r before using the sysfs interface.  It is nice to have that
> with a proper timestamp because a lot of the failures are in the driver suspend
> and resume paths.  I could easily change the options to:

The timekeeper suspends/resumes in the syscore section, so the driver part is
not affected.
 
> 0 = disable
> 1 = local clock (which along with 0 would maintain the current state of things)
> 2 = monotonic
> 3 = real

Yes, that works.

Btw, you need to document, that REAL can occasionally provide a wrong value on
32bit machines in case that a concurrent update of the realtime offset happens
(settimeofday, leap seconds ...). That's because we access real_offset w/o the
seqcount protection. It's probably hard to achieve, but it might happen.

Thanks,

	tglx