Messages in this thread | | | Date | Wed, 23 Feb 2011 07:52:34 -0800 | From | Darren Hart <> | Subject | Re: [PATCH 2/2] sched: allow users with rtprio rlimit to change from SCHED_IDLE policy |
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On 02/23/2011 03:17 AM, Peter Zijlstra wrote: > On Wed, 2011-02-23 at 12:13 +0100, Ingo Molnar wrote: >> * Peter Zijlstra<peterz@infradead.org> wrote: >> >>> On Tue, 2011-02-22 at 13:04 -0800, Darren Hart wrote: >>>> As it stands, users with rtprio rlimit permissions can change their policy from >>>> SCHED_OTHER to SCHED_FIFO and back. They can change to SCHED_IDLE, but not back >>>> to SCHED_FIFO. If they have the rtprio permission, they should be able to. Once >>>> in SCHED_FIFO, they could go back to SCHED_OTHER. This patch allows users with >>>> rtprio permission to change out of SCHED_IDLE. >>>> >>> >>> Ingo, can you remember the rationale for this? >>> >>> The fact is that SCHED_IDLE is very near nice-20, and we can do: >>> >>> peterz@twins:~$ renice 5 -p $$ >>> 1867: old priority 0, new priority 5 >>> peterz@twins:~$ renice 0 -p $$ >>> 1867: old priority 5, new priority 0 >>> >>> Which would suggest that we should be able to return to SCHED_OTHER >>> RLIMIT_NICE-20. >> >> I dont remember anything subtle there - most likely we just forgot about that spot >> when adding RLIMIT_RTPRIO support. > > Ah, I was arguing we should allow it regardless of RLIMIT_RTPRIO, based > on RLIMIT_NICE, it is after all a change to SCHED_OTHER, not > SCHED_FIFO/RR.
So we need an OR test of RLIMIT_NICE | RLIMIT_RTPRIO ? The reason I keep coming back to RTPRIO is it allows the user to change to SCHED_(FIFO|RR), and from there they can change to anything they want - so why force two steps? Perhaps the argument is to keep the meaning of the RLIMITs precise, and if you want to go from IDLE->OTHER you had better properly set RLIMIT_NICE - maybe I just convinced myself.
Shall I respin the patch to reflect that?
-- Darren Hart Intel Open Source Technology Center Yocto Project - Linux Kernel
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