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

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Message-ID: <alpine.DEB.2.21.1907102114480.1758@nanos.tec.linutronix.de>
Date:   Wed, 10 Jul 2019 21:15:49 +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, 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.

Thanks,

	tglx