svn commit: r358483 - head/sys/compat/linux

[Yuri Pankov]

Tijl Coosemans wrote:
> Author: tijl
> Date: Sun Mar  1 13:12:04 2020
> New Revision: 358483
> URL: https://svnweb.freebsd.org/changeset/base/358483
> 
> Log:
>    linuxulator: Map scheduler priorities to Linux priorities.
>    
>    On Linux the valid range of priorities for the SCHED_FIFO and SCHED_RR
>    scheduling policies is [1,99].  For SCHED_OTHER the single valid priority is
>    0.  On FreeBSD it is [0,31] for all policies.  Programs are supposed to
>    query the valid range using sched_get_priority_(min|max), but of course some
>    programs assume the Linux values are valid.
>    
>    This commit adds a tunable compat.linux.map_sched_prio.  When enabled
>    sched_get_priority_(min|max) return the Linux values and sched_setscheduler
>    and sched_(get|set)param translate between FreeBSD and Linux values.
>    
>    Because there are more Linux levels than FreeBSD levels, multiple Linux
>    levels map to a single FreeBSD level, which means pre-emption might not
>    happen as it does on Linux, so the tunable allows to disable this behaviour.
>    It is enabled by default because I think it is unlikely that anyone runs
>    real-time software under Linux emulation on FreeBSD that critically relies
>    on correct pre-emption.
>    
>    This fixes FMOD, a commercial sound library used by several games.
>    
>    PR:		240043
>    Tested by:	Alex S <iwtcex at gmail.com>
>    Reviewed by:	dchagin
>    MFC after:	2 weeks
>    Differential Revision:	https://reviews.freebsd.org/D23790
> 
> Modified:
>    head/sys/compat/linux/linux_misc.c
>    head/sys/compat/linux/linux_misc.h
> 
> Modified: head/sys/compat/linux/linux_misc.c
> ==============================================================================
> --- head/sys/compat/linux/linux_misc.c	Sun Mar  1 12:34:27 2020	(r358482)
> +++ head/sys/compat/linux/linux_misc.c	Sun Mar  1 13:12:04 2020	(r358483)
> @@ -144,6 +144,11 @@ struct l_pselect6arg {
>   	l_size_t	ss_len;
>   };
>   
> +static bool map_sched_prio = true;
> +SYSCTL_BOOL(_compat_linux, OID_AUTO, map_sched_prio, CTLFLAG_RDTUN,
> +    &map_sched_prio, 0, "Map scheduler priorities to Linux priorities "
> +    "(not POSIX compliant)");

I'm seeing the following in the log:

sysctl_warn_reuse: can't re-use a leaf (compat.linux.map_sched_prio)!

Should this be done for both linux and linux32 (when one exists) or made 
to install one time only?