linux-kernel - Re: [PATCH v8 clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog

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Date:   Fri, 16 Apr 2021 15:38:48 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, john.stultz@...aro.org,
        sboyd@...nel.org, corbet@....net, Mark.Rutland@....com,
        maz@...nel.org, kernel-team@...com, neeraju@...eaurora.org,
        ak@...ux.intel.com, Chris Mason <clm@...com>
Subject: Re: [PATCH v8 clocksource 1/5] clocksource: Provide module
 parameters to inject delays in watchdog

On Fri, Apr 16, 2021 at 10:10:51PM +0200, Thomas Gleixner wrote:
> On Tue, Apr 13 2021 at 21:35, Paul E. McKenney wrote:
> >  
> > +static int inject_delay_freq;
> > +module_param(inject_delay_freq, int, 0644);
> > +static int inject_delay_run = 1;
> > +module_param(inject_delay_run, int, 0644);
> 
> int? Can't we just make them 'unsigned int'? Negative values are not
> that useful.
> 
> > +static int max_read_retries = 3;
> > +module_param(max_read_retries, int, 0644);
> 
> max_read_retries is unused here. Should be in the patch which actually
> uses it.

Good point, I will make all three unsigned int and move max_read_retries
to 2/5 ("clocksource: Retry clock read if long delays detected").

> > +static void clocksource_watchdog_inject_delay(void)
> > +{
> > +	int i;
> > +	static int injectfail = -1;
> > +
> > +	if (inject_delay_freq <= 0 || inject_delay_run <= 0)
> > +		return;
> > +	if (injectfail < 0 || injectfail > INT_MAX / 2)
> > +		injectfail = inject_delay_run;
> > +	if (!(++injectfail / inject_delay_run % inject_delay_freq)) {
> 
> Operator precedence based cleverness is really easy to parse - NOT!
> 
> > +		pr_warn("%s(): Injecting delay.\n", __func__);
> > +		for (i = 0; i < 2 * WATCHDOG_THRESHOLD / NSEC_PER_MSEC; i++)
> > +			udelay(1000);
> > +		pr_warn("%s(): Done injecting delay.\n", __func__);
> > +	}
> > +
> > +	WARN_ON_ONCE(injectfail < 0);
> > +}
> 
> Brain melt stage reached by now.
> 
>         static unsigned int invocations, injections;
> 
>         if (!inject_delay_period || !inject_delay_repeat)
>         	return;
> 
>         if (!(invocations % inject_delay_period)) {
>         	mdelay(2 * WATCHDOG_THRESHOLD / NSEC_PER_MSEC);
>                 if (++injections < inject_delay_repeat)
>                 	return;
>                 injections = 0;
>         }
> 
>         invocations++;
> }
> 
> Hmm?

That is quite a bit nicer than the interacting parameters that I
had.  I will rework along these lines.

							Thanx, Paul