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From: Thomas Gleixner <tglx@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Calvin Owens <calvin@wbinvd.org>,
 Anna-Maria Behnsen <anna-maria@linutronix.de>, Frederic Weisbecker
 <frederic@kernel.org>, Ingo Molnar <mingo@kernel.org>, John Stultz
 <jstultz@google.com>, Stephen Boyd <sboyd@kernel.org>, Alexander Viro
 <viro@zeniv.linux.org.uk>, Christian Brauner <brauner@kernel.org>, Jan
 Kara <jack@suse.cz>, linux-fsdevel@vger.kernel.org, Sebastian Reichel
 <sre@kernel.org>, linux-pm@vger.kernel.org, Pablo Neira Ayuso
 <pablo@netfilter.org>, Florian Westphal <fw@strlen.de>, Phil Sutter
 <phil@nwl.cc>, netfilter-devel@vger.kernel.org, coreteam@netfilter.org
Subject: Re: [patch 01/12] clockevents: Prevent timer interrupt starvation
In-Reply-To: <20260407094206.GL2872@noisy.programming.kicks-ass.net>
References: <20260407083219.478203185@kernel.org>
 <20260407083247.562657657@kernel.org>
 <20260407094206.GL2872@noisy.programming.kicks-ass.net>
Date: Tue, 07 Apr 2026 13:30:42 +0200
Message-ID: <87o6jv57od.ffs@tglx>
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On Tue, Apr 07 2026 at 11:42, Peter Zijlstra wrote:
> On Tue, Apr 07, 2026 at 10:54:17AM +0200, Thomas Gleixner wrote:
>> @@ -324,16 +324,23 @@ int clockevents_program_event(struct clo
>>  		return dev->set_next_ktime(expires, dev);
>>  
>>  	delta = ktime_to_ns(ktime_sub(expires, ktime_get()));
>>  
>> +	if (delta > (int64_t)dev->min_delta_ns) {
>> +		delta = min(delta, (int64_t) dev->max_delta_ns);
>> +		clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
>> +		if (!dev->set_next_event((unsigned long) clc, dev))
>> +			return 0;
>> +	}
>>  
>> +	if (dev->next_event_forced)
>> +		return 0;
>>  
>> +	if (dev->set_next_event(dev->min_delta_ticks, dev)) {
>> +		if (!force || clockevents_program_min_delta(dev))
>> +			return -ETIME;
>> +	}
>> +	dev->next_event_forced = 1;
>> +	return 0;
>>  }
>
> Looking at the implementation of clockevents_program_min_delta() doing
> that dev->set_next_event(dev->min_delta_ticks,) right before it seems a
> bit daft.
>
> But yes, this is effectively also what the old code did.

yes. I looked at that and didn't come up with a good plan.

> The only thing that seems to be different, is that the old code would
> return the ->set_next_event() error code, rather than 0 in the !force
> case.

You mean when dev->next_event_forced is set and the set_event() callback
above failed?

Thanks,

        tglx