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

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Message-ID: <rdEqY1XYnE6kLSvXRjXReSAey0SEwMDUvqQRqLheIM99LpGH8pmv1ngZsNAkW1-DEHQhERga-rxGfTbuhL6FW_aEdo1DvWaOgncii1KmupY=@pm.me>
Date: Mon, 16 Sep 2024 19:48:54 +0000
From: Michael Pratt <mcpratt@...me>
To: Peter Zijlstra <peterz@...radead.org>
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

one more detail I forgot:
it actually would not be compliant for niceness as the input...

On Monday, September 16th, 2024 at 15:23, Michael Pratt <mcpratt@...me> wrote:

> On Monday, September 16th, 2024 at 07:13, Peter Zijlstra <peterz@...radead.org> wrote:
>
> > Worse, you're proposing a nice ABI that is entirely different from the
> > normal [-20,19] range.
> 
> ...
> ...
> ...
> 
> Otherwise, we have a confusing conflation between the meaning of the two values,
> where a value of 19 makes sense for niceness, but is obviously invalid for priority
> for SCHED_NORMAL, and a negative value makes sense for niceness, but is obviously invalid
> for priority in any policy.
> 

POSIX doesn't allow a negative value for the ABI at all:

  If successful, the sched_get_priority_max() and sched_get_priority_min() functions return
  the appropriate maximum or minimum values, respectively.
  If unsuccessful, they return a value of -1 and set errno to indicate the error.

--
MCP