[PATCH] sched_rr_get_interval.2: update Linux notes

[PATCH] sched_rr_get_interval.2: update Linux notes

[Clemens Ladisch]

Signed-off-by: Clemens Ladisch <clemens-P6GI/4k7KOmELgA04lAiVw@public.gmane.org>

--- a/man2/sched_rr_get_interval.2
+++ b/man2/sched_rr_get_interval.2
@@ -98,18 +98,24 @@
 .\" for SCHED_RR processes.  For RR processes the timeslice is always
 .\" DEF_TIMESLICE, or 0.1 secs.
 .\" Was the following really true for older kernels?
-.\" Must build a 2.6.8 kernel and retest, and rewrite the following text
-.\" appropriately.
+.\" It is again true for at least Linux 2.6.12, but stopped in 2.6.24.
 POSIX does not specify any mechanism for controlling the size of the
 round-robin time quantum.
 However, Linux provides a (nonportable) method of doing this.
-The quantum can be controlled by adjusting the process's nice value (see
+The quantum of both
+.B SCHED_RR
+and
+.B SCHED_OTHER
+processes can be controlled by adjusting the process's nice value (see
 .BR setpriority (2)).
 Assigning a negative (i.e., high) nice value results in a longer quantum;
 assigning a positive (i.e., low) nice value results in a shorter quantum.
 The default quantum is 0.1 seconds;
 the degree to which changing the nice value affects the
 quantum has varied somewhat across kernel versions.
+Since Linux 2.6.24, the
+.B SCHED_RR
+quantum cannot be modified.
 .\" .SH BUGS
 .\" As of Linux 1.3.81
 .\" .BR sched_rr_get_interval ()
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Re: [PATCH] sched_rr_get_interval.2: update Linux notes

[Michael Kerrisk]

Hello Clemens,

On Tue, Oct 11, 2011 at 1:40 PM, Clemens Ladisch <clemens-P6GI/4k7KOmELgA04lAiVw@public.gmane.org> wrote:
> Signed-off-by: Clemens Ladisch <clemens-P6GI/4k7KOmELgA04lAiVw@public.gmane.org>

Thanks for this. Do you have a pointer to the relevant kernel commit?

Cheers,

Michael


> --- a/man2/sched_rr_get_interval.2
> +++ b/man2/sched_rr_get_interval.2
> @@ -98,18 +98,24 @@
>  .\" for SCHED_RR processes.  For RR processes the timeslice is always
>  .\" DEF_TIMESLICE, or 0.1 secs.
>  .\" Was the following really true for older kernels?
> -.\" Must build a 2.6.8 kernel and retest, and rewrite the following text
> -.\" appropriately.
> +.\" It is again true for at least Linux 2.6.12, but stopped in 2.6.24.
>  POSIX does not specify any mechanism for controlling the size of the
>  round-robin time quantum.
>  However, Linux provides a (nonportable) method of doing this.
> -The quantum can be controlled by adjusting the process's nice value (see
> +The quantum of both
> +.B SCHED_RR
> +and
> +.B SCHED_OTHER
> +processes can be controlled by adjusting the process's nice value (see
>  .BR setpriority (2)).
>  Assigning a negative (i.e., high) nice value results in a longer quantum;
>  assigning a positive (i.e., low) nice value results in a shorter quantum.
>  The default quantum is 0.1 seconds;
>  the degree to which changing the nice value affects the
>  quantum has varied somewhat across kernel versions.
> +Since Linux 2.6.24, the
> +.B SCHED_RR
> +quantum cannot be modified.
>  .\" .SH BUGS
>  .\" As of Linux 1.3.81
>  .\" .BR sched_rr_get_interval ()
>



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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Re: [PATCH] sched_rr_get_interval.2: update Linux notes

[Clemens Ladisch]

On 10/11/2011 04:52 PM, Michael Kerrisk wrote:
> On Tue, Oct 11, 2011 at 1:40 PM, Clemens Ladisch <clemens-P6GI/4k7KOmELgA04lAiVw@public.gmane.org> wrote:
>> Signed-off-by: Clemens Ladisch <clemens-P6GI/4k7KOmELgA04lAiVw@public.gmane.org>
>
> Thanks for this. Do you have a pointer to the relevant kernel commit?

http://git.kernel.org/linus/a4ec24b48dde


Regards,
Clemens
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Re: [PATCH] sched_rr_get_interval.2: update Linux notes

[Michael Kerrisk]

Hello Clemens,

Thanks once again for this patch. See my notes below.

On Tue, Oct 11, 2011 at 1:40 PM, Clemens Ladisch <clemens-P6GI/4k7KOmELgA04lAiVw@public.gmane.org> wrote:
> Signed-off-by: Clemens Ladisch <clemens-P6GI/4k7KOmELgA04lAiVw@public.gmane.org>
>
> --- a/man2/sched_rr_get_interval.2
> +++ b/man2/sched_rr_get_interval.2
> @@ -98,18 +98,24 @@
>  .\" for SCHED_RR processes.  For RR processes the timeslice is always
>  .\" DEF_TIMESLICE, or 0.1 secs.
>  .\" Was the following really true for older kernels?
> -.\" Must build a 2.6.8 kernel and retest, and rewrite the following text
> -.\" appropriately.
> +.\" It is again true for at least Linux 2.6.12, but stopped in 2.6.24.

(At this point, I think we can simply drop these source code comments
altogether. Your patch supplied the needed details.)

>  POSIX does not specify any mechanism for controlling the size of the
>  round-robin time quantum.
>  However, Linux provides a (nonportable) method of doing this.
> -The quantum can be controlled by adjusting the process's nice value (see
> +The quantum of both
> +.B SCHED_RR
> +and
> +.B SCHED_OTHER
> +processes can be controlled by adjusting the process's nice value (see

I don't really want to document the SCHED_OTHER detail here. This page
is about SCHED_RR processes. The point about SCHED_OTHER is an
implementation detail that isn't relevant to SCHED_RR.

>  .BR setpriority (2)).
>  Assigning a negative (i.e., high) nice value results in a longer quantum;
>  assigning a positive (i.e., low) nice value results in a shorter quantum.
>  The default quantum is 0.1 seconds;
>  the degree to which changing the nice value affects the
>  quantum has varied somewhat across kernel versions.
> +Since Linux 2.6.24, the
> +.B SCHED_RR
> +quantum cannot be modified.

Here's the goodies!

>  .\" .SH BUGS
>  .\" As of Linux 1.3.81
>  .\" .BR sched_rr_get_interval ()

So, I tweaked your patch somewhat, and applied the patch below for
man-pages-3.36.

Cheers,

Michael

--- a/man2/sched_rr_get_interval.2
+++ b/man2/sched_rr_get_interval.2
@@ -102,16 +102,9 @@ is available define
 in
 .IR <unistd.h> .
 .SS Linux Notes
-.\" FIXME
-.\" From at least Linux 2.6.9, the following is no longer true
-.\" for SCHED_RR processes.  For RR processes the timeslice is always
-.\" DEF_TIMESLICE, or 0.1 secs.
-.\" Was the following really true for older kernels?
-.\" Must build a 2.6.8 kernel and retest, and rewrite the following text
-.\" appropriately.
 POSIX does not specify any mechanism for controlling the size of the
 round-robin time quantum.
-However, Linux provides a (nonportable) method of doing this.
+Older Linux kernels provide a (nonportable) method of doing this.
 The quantum can be controlled by adjusting the process's nice value (see
 .BR setpriority (2)).
 Assigning a negative (i.e., high) nice value results in a longer quantum;
@@ -119,6 +112,11 @@ assigning a positive (i.e., low) nice value
results in a shorter quantum.
 The default quantum is 0.1 seconds;
 the degree to which changing the nice value affects the
 quantum has varied somewhat across kernel versions.
+Since Linux 2.6.24,
+.\" commit a4ec24b48ddef1e93f7578be53270f0b95ad666c
+the
+.BR SCHED_RR
+quantum cannot be modified.
 .\" .SH BUGS
 .\" As of Linux 1.3.81
 .\" .BR sched_rr_get_interval ()

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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