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

From: Thomas Gleixner
Date: Wed Jan 27 2016 - 04:40:30 EST

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.