linux-kernel - Re: [patch V6 07/11] rseq: Implement time slice extension enforcement timer

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Message-ID: <20260119100143.GO830755@noisy.programming.kicks-ass.net>
Date: Mon, 19 Jan 2026 11:01:43 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>, Jonathan Corbet <corbet@....net>,
	Prakash Sangappa <prakash.sangappa@...cle.com>,
	Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	Randy Dunlap <rdunlap@...radead.org>,
	Ron Geva <rongevarg@...il.com>, Waiman Long <longman@...hat.com>
Subject: Re: [patch V6 07/11] rseq: Implement time slice extension
 enforcement timer

On Sun, Jan 18, 2026 at 11:46:18AM +0100, Thomas Gleixner wrote:
> On Fri, Jan 16 2026 at 19:15, Peter Zijlstra wrote:
> > On Fri, Dec 19, 2025 at 11:05:17AM +0100, Peter Zijlstra wrote:
> >
> >> I was thinking that perhaps the hrtimer tracepoints, filtered on this
> >> specific timer, might just do. Arming the timer is the point where the
> >> extension is granted, cancelling the timer is on the slice_yield() (or
> >> any other random syscall :/), and the timer actually firing is on fail.
> >
> > Here, I google pasted this together. I don't actually speak much snake
> > (as you well know). Nor does it fully work; the handle_expire() thing is
> > busted, I definitely have expire entries in the trace, but they're not
> > showing up.
> 
> You want the below. Then you get:
> 
> Task: slice_test    Mean: 350.266 ns
>   Latency (us)    | Count
>   ------------------------------
>   EXPIRED         | 238
>   0 us            | 143189
>   1 us            | 167
>   2 us            | 26
>   3 us            | 11
>   4 us            | 28
>   5 us            | 31
>   6 us            | 22
>   7 us            | 23
>   8 us            | 32
>   9 us            | 16
>   10 us           | 35
> 
> Thanks
> 
>         tglx
> ---
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -1742,7 +1742,7 @@ static void __run_hrtimer(struct hrtimer
>  
>  	lockdep_assert_held(&cpu_base->lock);
>  
> -	debug_deactivate(timer);
> +	debug_hrtimer_deactivate(timer);
>  	base->running = timer;

D'0h.

I suppose doing this makes more sense than fixing the script. Want me to
write it up?