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

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Message-ID: <20190710113609.7b63c5d6@gandalf.local.home>
Date:   Wed, 10 Jul 2019 11:36:09 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sodagudi Prasad <psodagud@...eaurora.org>
Cc:     tglx@...utronix.de, 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

[ 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;

This will prevent other issues happening by modifying sched_clock(),
specifically, screwing up the scheduler (what sched_clock()'s main
purpose is for). We don't want the scheduler to think that a process
was running for hours when it has spent most of that time in the
suspend state. Which is probably your answer to why it was designed
that way.

-- Steve