linux-kernel - Re: Experiencing freezes with kernel 4.16.3 on a desktop with E5500 CPU (bisect included)

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Message-ID: <20180423155801.GQ4129@hirez.programming.kicks-ass.net>
Date:   Mon, 23 Apr 2018 17:58:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Diego Viola <diego.viola@...il.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        len.brown@...el.com, rui.zhang@...el.com,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: Experiencing freezes with kernel 4.16.3 on a desktop with E5500
 CPU (bisect included)

On Mon, Apr 23, 2018 at 02:38:47PM +0200, Peter Zijlstra wrote:

> @@ -142,6 +152,13 @@ static void __clocksource_unstable(struct clocksource *cs)
>  	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
>  	cs->flags |= CLOCK_SOURCE_UNSTABLE;
>  
> +	if (list_empty(&cs->list)) {
> +		cs->rating = 0;
> +		return;
> +	}
> +
> +	__clocksource_change_rating(cs, 0);
> +
>  	if (cs->mark_unstable)
>  		cs->mark_unstable(cs);
>  

Thomas, we could not find the de-rate stuff, but the above can be
simplified; what happens is:

	cs->flags |= UNSTABLE;
	schedule_work(&watchdog_work)
	  kthread_run(clocksource_watchdog_kthread)
	    __clocksource_watchdog_kthread()
	      if (cs->flags & UNSTABLE)
	        __clocksource_change_rating()
	   clocksource_select()