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

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Message-ID: <87zf6b19mt.ffs@tglx>
Date: Sun, 18 Jan 2026 11:46:18 +0100
From: Thomas Gleixner <tglx@...nel.org>
To: Peter Zijlstra <peterz@...radead.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 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;

 	/*