I have been reviewing how OP‑TEE is implemented and how secure‑world
invocations behave. The goal was to determine whether an OP‑TEE call can
delay the Linux side and introduce latency depending on the time spent
in the secure world.
Similar latency effects are already known for EFI runtime services, but
this was not documented. To mitigate the impact, EFI runtime invocations
can be restricted to specific CPUs so that real‑time workloads on other
CPUs remain unaffected. This mechanism, however, is only described in
the commit that introduced it.
This change adds a firmware section that documents these behaviours
explicitly. It highlights cases where firmware can delay the kernel,
information that may be unfamiliar to some users and surprising-or
concerning-to others.
Assisted-by: Microsoft-Copilot
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260718175041.QXn9iOFK@linutronix.de>
Add a configuration guide for real-time kernels.
List all Kconfig options that are recommended to be either enabled or
disabled. Explicitly add a table of contents at the top of the document,
so that all the options can be seen in a glance.
Whenever appropriate, link to other kernel guides; e.g. cpuidle, cpufreq,
power management, workqueues, and no_hz.
Add a summary at the end of the document warning users that there is no
"one size fits all solution" for configuring a real-time system.
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260804141541.747704-2-darwi@linutronix.de>
The man page reference appeared twice - once as plain text and
once as a hyperlink. Remove the plain text duplicate.
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260531141823.4118954-1-costa.shul@redhat.com>
Commit 4843a45ef9fe8 ("entry: Rename "kvm" entry code assets to "virt"
to genericize APIs") renames the config KVM_XFER_TO_GUEST_WORK to
VIRT_XFER_TO_GUEST_WORK.
Adjust the documentation to the current situation, and specifically
refer to the new name of the config.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20251127154343.292156-3-bigeasy@linutronix.de>
Some thoughts on hardware that is used for real-time workload. Certainly
not complete but should cover some of the import topics such as:
- Main memory, caches and the possiblie control given by the hardware.
- What could happen by putting critical hardware behind USB or VirtIO.
- Allowing real-time tasks to consume the CPU entirely without giving
the system some time to breath.
- Networking with what the kernel provides.
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20251127154343.292156-2-bigeasy@linutronix.de>
The documents explain the design concepts behind PREEMPT_RT and highlight key
differences necessary to achieve it.
It also include a list of requirements that must be fulfilled to support
PREEMPT_RT on a given architecture.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[jc: tweaked "how they differ" section head]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250815093858.930751-4-bigeasy@linutronix.de
