sched/rt: Show the 'sched_rr_timeslice' SCHED_RR timeslice tuning knob in milliseconds

[ Upstream commit 975e155e ]

We added the 'sched_rr_timeslice_ms' SCHED_RR tuning knob in this commit:

  ce0dbbbb

 ("sched/rt: Add a tuning knob to allow changing SCHED_RR timeslice")

... which name suggests to users that it's in milliseconds, while in reality
it's being set in milliseconds but the result is shown in jiffies.

This is obviously confusing when HZ is not 1000, it makes it appear like the
value set failed, such as HZ=100:

  root# echo 100 > /proc/sys/kernel/sched_rr_timeslice_ms
  root# cat /proc/sys/kernel/sched_rr_timeslice_ms
  10

Fix this to be milliseconds all around.

Signed-off-by: Shile Zhang <shile.zhang@nokia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1485612049-20923-1-git-send-email-shile.zhang@nokia.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>