linux-kernel - Re: [PATCH v3] clocksource: Scale the max retry number of watchdog read according to CPU numbers

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Message-ID: <ZdNnjdNTjtvpbGH0@feng-clx.sh.intel.com>
Date: Mon, 19 Feb 2024 22:37:01 +0800
From: Feng Tang <feng.tang@...el.com>
To: Thomas Gleixner <tglx@...utronix.de>
CC: John Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>,
	<paulmck@...nel.org>, Waiman Long <longman@...hat.com>, Peter Zijlstra
	<peterz@...radead.org>, <linux-kernel@...r.kernel.org>, Jin Wang
	<jin1.wang@...el.com>
Subject: Re: [PATCH v3] clocksource: Scale the max retry number of watchdog
 read according to CPU numbers

Hi Thomas,

On Mon, Feb 19, 2024 at 12:32:05PM +0100, Thomas Gleixner wrote:
> On Mon, Jan 29 2024 at 21:45, Feng Tang wrote:
> > +static inline long clocksource_max_watchdog_read_retries(void)
> > +{
> > +	long max_retries = max_cswd_read_retries;
> > +
> > +	if (max_cswd_read_retries <= 0) {
> > +		/* santity check for user input value */
> > +		if (max_cswd_read_retries != -1)
> > +			pr_warn_once("max_cswd_read_retries was set with an invalid number: %ld\n",
> > +				max_cswd_read_retries);
> > +
> > +		max_retries = ilog2(num_online_cpus()) + 1;
> 
> I'm getting tired of these knobs and the horrors behind them. Why not
> simply doing the obvious:
> 
>        retries = ilog2(num_online_cpus()) + 1;
> 
> and remove the knob alltogether?

Thanks for the suggestion! Yes, this makes sense to me. IIUC, the
'max_cswd_read_retries' was introduced mainly to cover different
platforms' requirement, which could now be covered by the new
self-adaptive number.

If there is no concern from other developers, I will send a new
version in this direction.

Thanks,
Feng

> 
> Thanks,
> 
>         tglx