linux-kernel - SCHED_DEADLINE, sched_getscheduler(), and sched

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Message-ID: <CAKgNAkiA23kAFyXQkFV4z0aUE+y5K7AFNwRW+4LqwAyVj=tQtQ@mail.gmail.com>
Date:	Mon, 12 May 2014 14:09:58 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Juri Lelli <juri.lelli@...il.com>,
	Dario Faggioli <raistlin@...ux.it>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-man <linux-man@...r.kernel.org>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: SCHED_DEADLINE, sched_getscheduler(), and sched_getparam()

Hi Peter,

Looking at the code of sched_getparam() and sched_setscheduler() (to
see what might need to land in the man pagea with respect to
SCHED_DEADLINE changes), I see that the former fails (EINVAL) if the
target is a SCHED_DEADLINE process, while the latter succeeds
(returning SCHED_DEADLINE).

The sched_setscheduler() seems fine, but what's the rationale for
having sched_getparam() fail in this case, rather than just returning
a sched_priority of zero (since sched_priority is in any case unused,
as for SCHED_OTHER, right)? My point is that the change seems to
needlessly break applications that employ sched_getparam(). Maybe I am
missing something...

Cheers,

Michael

-- 
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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