Re: [PATCH v2 2/5] man/man7/sched.7: Update the real-time section
From: Alejandro Colomar <alx@kernel.org>
Date: 2025-10-15 21:40:33
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Hi Sebastian, On Mon, Sep 15, 2025 at 04:13:02PM +0200, Sebastian Andrzej Siewior wrote:
Update the outdated information: - The PREEMPT_RT patch is merged. The patch continues to exist (as of now) but is not mandatory. - The patch can be still downloaded but most people use the git tree these days. Add a reference to it. - CONFIG_PREEMPT_DESKTOP was never thing as far as I remember. It was always CONFIG_PREEMPT and its description referred to "low latency desktop". - Within the PREEMPT-RT patch there was a brief window which introduced PREEMPT_RT_BASE and PREEMPT_RT_FULL. I am going to ignore this. - The introduction of PREEMPT_LAZY in 6.13 moved PREEMPT_RT from a preemption model to an option. - The mentioned wiki is deprecated. Update the URL to the new one. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Thanks! I've applied the patch, with the following amendment: diff --git i/man/man7/sched.7 w/man/man7/sched.7 index 51300d611..9622c1824 100644 --- i/man/man7/sched.7 +++ w/man/man7/sched.7 @@ -960,18 +960,18 @@ .SS Real-time features in the mainline Linux kernel or cloned from a git tree .UR https://git.kernel.org\:/pub\:/scm\:/linux\:/kernel\:/git\:/rt\:/linux-stable-rt.git .UE . -The individual releases are maintained as long as -the matching LTS kernel is maintained. +The individual releases are maintained +as long as the matching LTS kernel is maintained. .P -Since 6.12 it possible to enable the real-time preemption +Since Linux 6.12 it possible to enable the real-time preemption without the need for any patches. The .I realtime\-patch continues to exist and contains support -for not yet integrated architectures, -drivers and features that are in development. +for not-yet-integrated architectures, +drivers, and features that are in development. .P -Since 6.13 real-time becomes an option +Since Linux 6.13 real-time became an option and not a preemption model. With this change, the following preemption models are available: @@ -982,13 +982,13 @@ .SS Real-time features in the mainline Linux kernel .BR CONFIG_PREEMPT_LAZY . The real-time capabilities can be enabled with the option .B CONFIG_PREEMPT_RT -and the preemption model be set to either +and the preemption model can be set to either .B CONFIG_PREEMPT or .BR CONFIG_PREEMPT_LAZY . The latter model is less eager to preempt .B SCHED_NORMAL -tasks in an attempt to reduce lock holder preemption. +tasks in an attempt to reduce lock-holder preemption. It does not affect real-time tasks. .P With Cheers, Alex
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--- man/man7/sched.7 | 58 ++++++++++++++++++++++++++++++++++-------------- 1 file changed, 41 insertions(+), 17 deletions(-)diff --git a/man/man7/sched.7 b/man/man7/sched.7 index 3299c21dc1ad8..db7753c9e912c 100644 --- a/man/man7/sched.7 +++ b/man/man7/sched.7@@ -933,16 +933,12 @@ the following to modify the autogroup nice value for .EE .in .SS Real-time features in the mainline Linux kernel -.\" FIXME . Probably this text will need some minor tweaking -.\" ask Carsten Emde about this. +.\" The archaeologist knows about v2.6.9-mm1-V0.1-realtime-preempt Since Linux 2.6.18, Linux is gradually becoming equipped with real-time capabilities, most of which are derived from the former .I realtime\-preempt patch set. -Until the patches have been completely merged into the -mainline kernel, -they must be installed to achieve the best real-time performance. These patches are named: .P .in +4n@@ -953,24 +949,52 @@ they must be installed to achieve the best real-time performance. .P and can be downloaded from .UR http://www.kernel.org\:/pub\:/linux\:/kernel\:/projects\:/rt/ +.UE +or cloned from a git tree +.UR https://git.kernel.org\:/pub\:/scm\:/linux\:/kernel\:/git\:/rt\:/linux-stable-rt.git .UE . +The individual releases are maintained as long as +the matching LTS kernel is maintained. .P -Without the patches and prior to their full inclusion into the mainline -kernel, the kernel configuration offers only the three preemption classes +Since 6.12 it possible to enable the real-time preemption +without the need for any patches. +The +.I realtime\-patch +continues to exist and contains support +for not yet integrated architectures, +drivers and features that are in development. +.P +Since 6.13 real-time becomes an option +and not a preemption model. +With this change, +the following preemption models are available: .BR CONFIG_PREEMPT_NONE , .BR CONFIG_PREEMPT_VOLUNTARY , +.BR CONFIG_PREEMPT , and -.B CONFIG_PREEMPT_DESKTOP -which respectively provide no, some, and considerable -reduction of the worst-case scheduling latency. -.P -With the patches applied or after their full inclusion into the mainline -kernel, the additional configuration item +.BR CONFIG_PREEMPT_LAZY . +The real-time capabilities can be enabled with the option .B CONFIG_PREEMPT_RT -becomes available. -If this is selected, Linux is transformed into a regular +and the preemption model be set to either +.B CONFIG_PREEMPT +or +.BR CONFIG_PREEMPT_LAZY . +The latter model is less eager to preempt +.B SCHED_NORMAL +tasks in an attempt to reduce lock holder preemption. +It does not affect real-time tasks. +.P +With +.B CONFIG_PREEMPT_RT +enabled, +Linux is transformed into a regular real-time operating system. -The FIFO and RR scheduling policies are then used to run a thread +The +.BR SCHED_FIFO , +.BR SCHED_RR , +and +.B SCHED_DEADLINE +scheduling policies are then used to run a thread with true real-time priority and a minimum worst-case scheduling latency. .SH NOTES The@@ -1032,5 +1056,5 @@ and .I \%Documentation/\:scheduler/\:sched\-nice\-design\:.txt .P Worth looking at: -.UR http://rt.wiki.kernel.org/\:index.php +.UR https://wiki.linuxfoundation.org/\:realtime/\:start .UE-- 2.51.0
-- <https://www.alejandro-colomar.es> Use port 80 (that is, <...:80/>).
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