linux-kernel - [PATCH 0/2] hrtimer: More fixes for handling of timer slack of rt tasks

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Message-Id: <20240805124116.21394-1-felix.moessbauer@siemens.com>
Date: Mon,  5 Aug 2024 14:41:14 +0200
From: Felix Moessbauer <felix.moessbauer@...mens.com>
To: linux-kernel@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	jan.kiszka@...mens.com,
	Felix Moessbauer <felix.moessbauer@...mens.com>
Subject: [PATCH 0/2] hrtimer: More fixes for handling of timer slack of rt tasks

This series fixes the (hopefully) last location of an incorrectly
handled timer slack on rt tasks in hrtimer_start_range_ns(), which was
uncovered by a userland change in glibc 2.33. Along that, the patch documents,
that currently all tasks with rt priority should ignore the timer slack.

For me, it is unclear though, if this behavior is actually intended, as
also PI boosted tasks that create or reprogram timers ignore the timer slack.
While I guess this does not have an effect in most cases, it is at least
a lost performance optimization chance. Instead, ignoring the timer
slack could be limited to tasks with RT/DL scheduling policies.

Best regards,
Felix Moessbauer
Siemens AG

Felix Moessbauer (2):
  hrtimer: Document, that PI boosted tasks have no timer slack
  hrtimer: Ignore slack time for RT tasks in hrtimer_start_range_ns()

 kernel/time/hrtimer.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

-- 
2.39.2