[PATCH] getpriority.2: Adjust the process priority range

[PATCH] getpriority.2: Adjust the process priority range

[Andrew Clayton]

The {get,set}priority man pages currently lists the process's priority
range as being from 40..1 however it should be 40..0 as 0 would be for
a nice of -20.

Signed-off-by: Andrew Clayton <andrew-gyMb1R/nBgN3uBD2Ct+Y/qxOck334EZe@public.gmane.org>
---

Perhaps the 40 should be 39 as the kernel seems to limit the nice range
from -20 to 19 in kernel/sched/core.c::set_user_nice().

 man2/getpriority.2 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/man2/getpriority.2 b/man2/getpriority.2
index b39bdcf..066cf75 100644
--- a/man2/getpriority.2
+++ b/man2/getpriority.2
@@ -197,7 +197,7 @@ The actual priority range varies between kernel versions.
 Linux before 1.3.36 had \-infinity..15.
 Since kernel 1.3.43, Linux has the range \-20..19.
 Within the kernel, nice values are actually represented
-using the corresponding range 40..1
+using the corresponding range 40..0
 (since negative numbers are error codes) and these are the values
 employed by the
 .BR setpriority ()
-- 
1.8.5.3

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Re: [PATCH] getpriority.2: Adjust the process priority range

[Michael Kerrisk (man-pages)]

Andrew,

On Wed, Mar 5, 2014 at 5:07 AM, Andrew Clayton
<andrew-gyMb1R/nBgN3uBD2Ct+Y/qxOck334EZe@public.gmane.org> wrote:
> The {get,set}priority man pages currently lists the process's priority
> range as being from 40..1 however it should be 40..0 as 0 would be for
> a nice of -20.


I don't think this is correct. Without actually re-checking the kernel
source, this is what I think is correct:

k-nice (the internal kernel value) has the range 40..1.
u-nice (the user-space value) has the range -20..+19

and u-nice = 20 - k-nice

(In fact, looking further down the man page, I see this is all
explained. Note that there is no +20 nice value on Linux.)

Cheers,

Michael


> Signed-off-by: Andrew Clayton <andrew-gyMb1R/nBgN3uBD2Ct+Y/qxOck334EZe@public.gmane.org>
> ---
>
> Perhaps the 40 should be 39 as the kernel seems to limit the nice range
> from -20 to 19 in kernel/sched/core.c::set_user_nice().
>
>  man2/getpriority.2 | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/man2/getpriority.2 b/man2/getpriority.2
> index b39bdcf..066cf75 100644
> --- a/man2/getpriority.2
> +++ b/man2/getpriority.2
> @@ -197,7 +197,7 @@ The actual priority range varies between kernel versions.
>  Linux before 1.3.36 had \-infinity..15.
>  Since kernel 1.3.43, Linux has the range \-20..19.
>  Within the kernel, nice values are actually represented
> -using the corresponding range 40..1
> +using the corresponding range 40..0
>  (since negative numbers are error codes) and these are the values
>  employed by the
>  .BR setpriority ()
> --
> 1.8.5.3
>



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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Re: [PATCH] getpriority.2: Adjust the process priority range

[Andrew Clayton]

On Wed, 5 Mar 2014 15:17:46 +0100, Michael Kerrisk (man-pages) wrote:

> Andrew,
> 
> On Wed, Mar 5, 2014 at 5:07 AM, Andrew Clayton
> <andrew-gyMb1R/nBgN3uBD2Ct+Y/qxOck334EZe@public.gmane.org> wrote:
> > The {get,set}priority man pages currently lists the process's
> > priority range as being from 40..1 however it should be 40..0 as 0
> > would be for a nice of -20.
> 
> 
> I don't think this is correct. Without actually re-checking the kernel
> source, this is what I think is correct:
> 
> k-nice (the internal kernel value) has the range 40..1.
> u-nice (the user-space value) has the range -20..+19
> 
> and u-nice = 20 - k-nice
> 
> (In fact, looking further down the man page, I see this is all
> explained. Note that there is no +20 nice value on Linux.)
> 
> Cheers,
> 
> Michael

Ok, thanks for the explanation. I was just confused by the above
because what user space seems to see is 39..0 (e,g the PRI column in
top, the 18th field in /proc/self/stat). Which is perhaps not really the
same thing were talking about here, which looking at a rt task has a
value of -100.

Cheers,
Andrew
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