Messages in this thread | | | Subject | Re: SCHED_IDLE documentation | From | Peter Zijlstra <> | Date | Tue, 04 Mar 2008 12:11:44 +0100 |
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On Mon, 2008-03-03 at 15:06 +0100, Michael Kerrisk wrote: > Ingo, > > On Mon, Mar 3, 2008 at 1:52 PM, Ingo Molnar <mingo@elte.hu> wrote: > > > > * Michael Kerrisk <mtk.manpages@googlemail.com> wrote: > > > > > > > > > * What's the difference between SCHED_IDLE and SCHED_BATCH? > > > > > > > > SCHED_BATCH can still have nice levels from -20 to +19, it is a > > > > modified SCHED_OTHER/SCHED_NORMAL for "throughput oriented" > > > > workloads. > > > > > > So, suppose we have two CPU intensive jobs, one SCHED_OTHER and the > > > other SCHED_BATCH. If they have the same nice value, will/should the > > > scheduler favour one over the other? > > > > yes - SCHED_BATCH does not modify the CPU usage proportion for > > CPU-intense tasks, it's their nice value that controls the proportion. > > What it will influence is wakeup behavior - i.e. wakeup-intense > > workloads should schedule less with SCHED_BATCH. (but how that is done > > is really fluid and will probably tweaked in the future.) > > > > Ingo > > So, I've tweaked the description of SCHED_BATCH in the > sched_setscheduler.2 man page, and added some text describing > SCHED_IDLE. Relevant excepts below. Does his look okay to you? > > SCHED_OTHER is the default universal time-sharing sched- > uler policy used by most processes. SCHED_BATCH is > intended for "batch" style execution of processes. > SCHED_IDLE is intended for running very low priority > background jobs. SCHED_FIFO and SCHED_RR are intended > for special time-critical applications that need precise > control over the way in which runnable processes are > selected for execution. > > Processes scheduled with SCHED_OTHER, SCHED_BATCH, or > SCHED_IDLE must be assigned the static priority 0. Pro- > cesses scheduled under SCHED_FIFO or SCHED_RR can have a > static priority in the range 1 to 99. > ... > > SCHED_BATCH: Scheduling batch processes > (Since Linux 2.6.16.) SCHED_BATCH can only be used at > static priority 0. This policy is similar to > SCHED_OTHER, except that it will cause the scheduler to > always assume that the process is CPU-intensive. Conse- > quently, the scheduler will apply a small scheduling > penalty with respect to wakeup behaviour, so that this > process is mildly disfavored in scheduling decisions. > This policy is useful for workloads that are non-interac- > tive, but do not want to lower their nice value, and for > workloads that want a deterministic scheduling policy > without interactivity causing extra preemptions (between > the workload's tasks). > > SCHED_IDLE: Scheduling very low priority jobs > (Since Linux 2.6.23.) SCHED_IDLE can only be used at > static priority 0; the process nice value has no influ- > ence for this policy. This policy is intended for run- > ning jobs at extremely low priority (lower even than a > +19 nice value with the SCHED_OTHER or SCHED_BATCH poli- > cies).
Your SCHED_BATCH and SCHED_IDLE descriptions seem at odds, in that your SCHED_IDLE description says you can run SCHED_BATCH +19, however your SCHED_BATCH description says you can only run at nice 0.
To clarify SCHED_BATCH _can_ indeed use the full nice range.
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