linux-kernel - Re: [RESEND PATCH] sched/syscalls: Allow setting niceness using sched

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Message-ID: <20240916111323.GX4723@noisy.programming.kicks-ass.net>
Date: Mon, 16 Sep 2024 13:13:23 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Michael Pratt <mcpratt@...me>
Cc: Ingo Molnar <mingo@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [RESEND PATCH] sched/syscalls: Allow setting niceness using
 sched_param struct

On Mon, Sep 16, 2024 at 05:08:49AM +0000, Michael Pratt wrote:
> From userspace, spawning a new process with, for example,
> posix_spawn(), only allows the user to work with
> the scheduling priority value defined by POSIX
> in the sched_param struct.
> 
> However, sched_setparam() and similar syscalls lead to
> __sched_setscheduler() which rejects any new value
> for the priority other than 0 for non-RT schedule classes,
> a behavior kept since Linux 2.6 or earlier.

Right, and the current behaviour is entirely in-line with the POSIX
specs.

I realize this might be a pain, but why should be change this spec
conforming and very long standing behaviour?

Worse, you're proposing a nice ABI that is entirely different from the
normal [-20,19] range.

Why do you feel this is the best way forward? Would not adding
POSIX_SPAWN_SETSCHEDATTR be a more future proof mechanism?