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

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Date: Mon, 19 Feb 2024 21:20:31 -0500
From: Waiman Long <longman@...hat.com>
To: Feng Tang <feng.tang@...el.com>, Thomas Gleixner <tglx@...utronix.de>
Cc: John Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>,
 paulmck@...nel.org, 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


On 2/19/24 09:37, Feng Tang wrote:
> 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.

I see no problem simplifying it.

Cheers,
Longman