From 60aa605dfce2976e54fa76e805ab0f221372d4d9 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 5 May 2009 17:50:21 +0200 Subject: sched: rt: document the risk of small values in the bandwidth settings Thomas noted that we should disallow sysctl_sched_rt_runtime == 0 for (!RT_GROUP) since the root group always has some RT tasks in it. Further, update the documentation to inspire clue. [ Impact: exclude corner-case sysctl_sched_rt_runtime value ] Reported-by: Thomas Gleixner Signed-off-by: Peter Zijlstra LKML-Reference: <20090505155436.863098054@chello.nl> Signed-off-by: Ingo Molnar --- Documentation/scheduler/sched-rt-group.txt | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'Documentation/scheduler') diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt index 5ba4d3fc625..eb74b014a3f 100644 --- a/Documentation/scheduler/sched-rt-group.txt +++ b/Documentation/scheduler/sched-rt-group.txt @@ -4,6 +4,7 @@ CONTENTS ======== +0. WARNING 1. Overview 1.1 The problem 1.2 The solution @@ -14,6 +15,23 @@ CONTENTS 3. Future plans +0. WARNING +========== + + Fiddling with these settings can result in an unstable system, the knobs are + root only and assumes root knows what he is doing. + +Most notable: + + * very small values in sched_rt_period_us can result in an unstable + system when the period is smaller than either the available hrtimer + resolution, or the time it takes to handle the budget refresh itself. + + * very small values in sched_rt_runtime_us can result in an unstable + system when the runtime is so small the system has difficulty making + forward progress (NOTE: the migration thread and kstopmachine both + are real-time processes). + 1. Overview =========== -- cgit v1.2.3 From f04d82b7e0c63d0251f9952a537a4bc4d73aa1a9 Mon Sep 17 00:00:00 2001 From: GeunSik Lim Date: Thu, 28 May 2009 10:36:14 +0900 Subject: sched: fix typo in sched-rt-group.txt file Fix typo about static priority's range. Kernel Space User Space =============================================================== 0(high) to 98(low) user RT priority 99(high) to 1(low) with SCHED_RR or SCHED_FIFO --------------------------------------------------------------- 99 sched_priority is not used in scheduling decisions(it must be specified as 0) --------------------------------------------------------------- 100(high) to 139(low) user nice -20(high) to 19(low) --------------------------------------------------------------- 140 idle task priority --------------------------------------------------------------- * ref) http://www.kernel.org/doc/man-pages/online/pages/man2/sched_setscheduler.2.html Signed-off-by: GeunSik Lim CC: Steven Rostedt Signed-off-by: Peter Zijlstra LKML-Reference: Signed-off-by: Ingo Molnar --- Documentation/scheduler/sched-rt-group.txt | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation/scheduler') diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt index eb74b014a3f..1df7f9cdab0 100644 --- a/Documentation/scheduler/sched-rt-group.txt +++ b/Documentation/scheduler/sched-rt-group.txt @@ -187,7 +187,7 @@ get their allocated time. Implementing SCHED_EDF might take a while to complete. Priority Inheritance is the biggest challenge as the current linux PI infrastructure is geared towards -the limited static priority levels 0-139. With deadline scheduling you need to +the limited static priority levels 0-99. With deadline scheduling you need to do deadline inheritance (since priority is inversely proportional to the deadline delta (deadline - now). -- cgit v1.2.3 From 19f594600110377ec4037fdf7fb93a25ec516212 Mon Sep 17 00:00:00 2001 From: Matt LaPlante Date: Mon, 27 Apr 2009 15:06:31 +0200 Subject: trivial: Miscellaneous documentation typo fixes Fix various typos in documentation txts. Signed-off-by: Matt LaPlante Signed-off-by: Jiri Kosina --- Documentation/scheduler/sched-nice-design.txt | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation/scheduler') diff --git a/Documentation/scheduler/sched-nice-design.txt b/Documentation/scheduler/sched-nice-design.txt index e2bae5a577e..3ac1e46d536 100644 --- a/Documentation/scheduler/sched-nice-design.txt +++ b/Documentation/scheduler/sched-nice-design.txt @@ -55,7 +55,7 @@ To sum it up: we always wanted to make nice levels more consistent, but within the constraints of HZ and jiffies and their nasty design level coupling to timeslices and granularity it was not really viable. -The second (less frequent but still periodically occuring) complaint +The second (less frequent but still periodically occurring) complaint about Linux's nice level support was its assymetry around the origo (which you can see demonstrated in the picture above), or more accurately: the fact that nice level behavior depended on the _absolute_ -- cgit v1.2.3