Re: [RFC patch 7/7] timekeeping: Hack to use fine grained timestamps during boot

From: Thomas Gleixner <tglx@linutronix.de>
To: Prarit Bhargava <prarit@redhat.com>
Cc: Petr Mladek <pmladek@suse.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linuxfoundation.org>,
	Mark Salyzyn <salyzyn@android.com>,
	Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Joe Perches <joe@perches.com>
Subject: Re: [RFC patch 7/7] timekeeping: Hack to use fine grained timestamps during boot
Date: Tue, 28 Nov 2017 19:47:09 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.20.1711281946140.2222@nanos> (raw)
In-Reply-To: <205229e2-fab4-31cb-60cd-f36bc2228804@redhat.com>

On Tue, 28 Nov 2017, Prarit Bhargava wrote:
> On 11/23/2017 07:58 AM, Petr Mladek wrote:
> > On Wed 2017-11-15 19:15:38, Thomas Gleixner wrote:
> >> For demonstration purposes only.
> >>
> >> Add a disgusting hack to work around the fact that high resolution clock
> >> MONOTONIC accessors are not available during early boot and return stale
> >> time stamps accross suspend/resume when the current clocksource is not
> >> flagged with CLOCK_SOURCE_SUSPEND_ACCESS_OK.
> >>
> >> Use local_clock() to provide timestamps in early boot and when the
> >> clocksource is not accessible after timekeeping_suspend(). In the
> >> suspend/resume case this might cause non monotonic timestamps.
> > 
> > I get the non-monotonic times even during boot:
> > 
> > [    0.026709] smp: Bringing up secondary CPUs ...
> > [    0.027973] x86: Booting SMP configuration:
> > [    0.028006] .... node  #0, CPUs:      #1
> > [    0.004000] kvm-clock: cpu 1, msr 1:3ff51041, secondary cpu clock
> >      ^^^^^^^^

Which is interesting as this should happen even w/o those patches. 

Thanks,

	tglx