linux-kernel - Re: [PATCH v2 3/6] hrtimer,sched: Add fuzzy hrtimer mode for HRTICK

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Message-ID: <20260123150428.25972f96@gandalf.local.home>
Date: Fri, 23 Jan 2026 15:04:50 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Juri Lelli <juri.lelli@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de,
 arnd@...db.de, anna-maria@...utronix.de, frederic@...nel.org,
 luto@...nel.org, mingo@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, linux-kernel@...r.kernel.org, oliver.sang@...el.com
Subject: Re: [PATCH v2 3/6] hrtimer,sched: Add fuzzy hrtimer mode for HRTICK

On Thu, 22 Jan 2026 14:12:28 +0100
Juri Lelli <juri.lelli@...hat.com> wrote:

> Hello,
> 
> On 21/01/26 17:20, Peter Zijlstra wrote:
> > Upon schedule() HRTICK will cancel the current timer, pick the next
> > task and reprogram the timer. When schedule() consistently triggers
> > due to blocking conditions instead of the timer, this leads to endless
> > reprogramming without ever firing.
> > 
> > Mitigate this with a new hrtimer mode: fuzzy (not really happy with
> > that name); this mode does two things:  
> 
> Does the more common (lazier :) 'lazy' work better?

I don't like either fuzzy or lazy.

Fuzzy makes me think of just random entries (for fuzz testing and such).

Lazy is to postpone things to do things less often.

What about "speculative"?  Like branch prediction and such. Where a timer
is expected to be used at a certain time but it may not be?

-- Steve