From: Steven Rostedt <rostedt@goodmis.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Xie Yuanbin <xieyuanbin1@huawei.com>,
arnd@arndb.de, linux-arm-kernel@lists.infradead.org,
linux-rt-devel@lists.linux.dev, linux@armlinux.org.uk,
tglx@linutronix.de
Subject: Re: [PATCH 4/5] ARM: Disable jump-label on PREEMPT_RT.
Date: Thu, 30 Oct 2025 05:46:26 -0400 [thread overview]
Message-ID: <20251030054626.7a897b29@gandalf.local.home> (raw)
In-Reply-To: <20251030075558.sUBj8_6U@linutronix.de>
On Thu, 30 Oct 2025 08:55:58 +0100
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> You can't really control when jump labels are enabled/ disabled. For
> instance this happens if you enable/ disable trace points.
> Arm64 and X86 replaced the stop_machine() logic with something else that
> does not affect latency in that magnitude. If Arm could something
> similar then fine but until then I don't see a way around it.
> There are other things that are disabled on PREEMPT_RT due to latency
> reasons such as transparent huge pages or expedited RCU.
But transparent huge pages and expedited RCU are not user controlled events.
Enabling function tracing was known to cause huge latency for a very long
time and it came from the PREEMPT_RT patch set. Heck, printk use to as well ;-)
Instead, we could print a message to the console stating that a huge
latency has just occurred due to user activation. Similar to what we used
to post when RT Throttling happened (I don't see that message anymore since
dl_server was added :-/).
-- Steve
next prev parent reply other threads:[~2025-10-30 9:45 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-29 15:59 [PATCH 0/5] ARM: Remaining PREEMPT_RT bits Sebastian Andrzej Siewior
2025-10-29 15:59 ` [PATCH 1/5] ARM: mm: fault: Move harden_branch_predictor() before interrupts are enabled Sebastian Andrzej Siewior
2025-10-29 15:59 ` [PATCH 2/5] ARM: mm: fault: Enable interrupts before invoking __do_user_fault() Sebastian Andrzej Siewior
2025-10-29 15:59 ` [PATCH 3/5] ARM: Disable FAST_GUP on PREEMPT_RT if HIGHPTE is also enabled Sebastian Andrzej Siewior
2025-10-30 15:15 ` Arnd Bergmann
2025-10-30 15:24 ` Sebastian Andrzej Siewior
2025-10-29 15:59 ` [PATCH 4/5] ARM: Disable jump-label on PREEMPT_RT Sebastian Andrzej Siewior
2025-10-30 2:39 ` Xie Yuanbin
2025-10-30 7:23 ` Sebastian Andrzej Siewior
2025-10-30 7:45 ` Xie Yuanbin
2025-10-30 7:55 ` Sebastian Andrzej Siewior
2025-10-30 9:46 ` Steven Rostedt [this message]
2025-10-30 9:56 ` Sebastian Andrzej Siewior
2025-10-30 10:05 ` Steven Rostedt
2025-10-30 10:38 ` Russell King (Oracle)
2025-10-30 11:10 ` Sebastian Andrzej Siewior
2025-10-30 15:24 ` Arnd Bergmann
2025-10-30 15:28 ` Sebastian Andrzej Siewior
2025-10-29 15:59 ` [PATCH 5/5] ARM: Allow to enable RT Sebastian Andrzej Siewior
2025-10-30 15:18 ` Arnd Bergmann
2025-10-30 15:22 ` Sebastian Andrzej Siewior
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