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/sched-rt-group.txt') diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt index 5ba4d3f..eb74b01 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 v1.1 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/sched-rt-group.txt') diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt index eb74b01..1df7f9c 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 v1.1