linux-kernel - Re: sched_clock and device suspend/resume

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Date:   Wed, 10 Jul 2019 21:22:35 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
cc:     Sodagudi Prasad <psodagud@...eaurora.org>,
        gregkh@...uxfoundation.org, john.stultz@...aro.org,
        chang-an.chen@...iatek.com, mingo@...nel.org, pmladek@...e.com,
        sergey.senozhatsky@...il.com, linux-kernel@...r.kernel.org,
        tsoni@...eaurora.org
Subject: Re: sched_clock and device suspend/resume

On Wed, 10 Jul 2019, Thomas Gleixner wrote:

> On Wed, 10 Jul 2019, Steven Rostedt wrote:
> > 
> > [ Removed the two emails that were bouncing ]
> > 
> > On Wed, 10 Jul 2019 21:06:57 +0200 (CEST)
> > Thomas Gleixner <tglx@...utronix.de> wrote:
> > 
> > > > > > sched_clock_continuous() ? (I know, horrible name), that simply keeps
> > > > > > track of the time delta at suspend and returns:
> > > > > > 
> > > > > > 	sched_clock() + delta;    
> > > > > 
> > > > > Which you get already when you do
> > > > > 
> > > > > # echo boot > /sys/kernel/debug/tracing/trace_clock
> > > > >   
> > > > 
> > > > So basically the answer here is to change printk to use
> > > > ktime_get_boot_fast_ns() instead of local_clock()?  
> > > 
> > > Aargh. That was tracing.
> > > 
> > > There was a patchset floating around which actually implemented that clock
> > > choice for sched_clock as well. Don't know why that was never merged.
> > 
> > Will it cause issues with the scheduler though. If it doesn't stop
> > during suspend, can't that make the scheduler think that processes were
> > using the CPU during the entire suspend and screw up the accounting?
> 
> Duh. My brain is not working.
> 
> Not sched_clock, the patches were for printk so you could select a printk
> clock. Can't find them right now.

Ah, we actually tried to merge them. Here is the full story:

  https://lore.kernel.org/lkml/alpine.DEB.2.20.1711131023170.1851@nanos/

Thanks,

	tglx