Messages in this thread | | | Date | Mon, 3 Mar 2008 15:06:55 +0100 | From | "Michael Kerrisk" <> | Subject | Re: SCHED_IDLE documentation |
| |
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).
Cheers,
Michael
-- Michael Kerrisk Maintainer of the Linux man-pages project http://www.kernel.org/doc/man-pages/ Want to report a man-pages bug? Look here: http://www.kernel.org/doc/man-pages/reporting_bugs.html
| |