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

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Date:   Wed, 10 Jul 2019 21:06:57 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
cc:     Sodagudi Prasad <psodagud@...eaurora.org>,
        pasha.tatashin@...cle.com, gregkh@...uxfoundation.org,
        sboyd@...eaurora.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:
> On Wed, 10 Jul 2019 20:35:32 +0200 (CEST)
> Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > On Wed, 10 Jul 2019, Steven Rostedt wrote:
> > 
> > > 
> > > [ Resending as your Cc was screwed up and caused my reply to mess up
> > >   the Cc list ]
> > > 
> > > On Wed, 10 Jul 2019 08:20:37 -0700
> > > Sodagudi Prasad <psodagud@...eaurora.org> wrote:
> > >   
> > > > Another option is printing the epoch/cycles information in every print 
> > > > statement similar to thread id or processor id added 
> > > > recently(CONFIG_PRINTK_CALLER). This can be avoided if we start 
> > > > accounting suspend time in sched_clock.  
> > > 
> > > Or another option is add a new clock that printk and tracing can use.
> > > tracing already can switch between clocks trivially.
> > > 
> > > 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.

Thanks,

	tglx