From 917b627d4d981dc614519d7b34ea31a976b14e12 Mon Sep 17 00:00:00 2001 From: Gregory Haskins Date: Mon, 29 Dec 2008 09:39:53 -0500 Subject: sched: create "pushable_tasks" list to limit pushing to one attempt The RT scheduler employs a "push/pull" design to actively balance tasks within the system (on a per disjoint cpuset basis). When a task is awoken, it is immediately determined if there are any lower priority cpus which should be preempted. This is opposed to the way normal SCHED_OTHER tasks behave, which will wait for a periodic rebalancing operation to occur before spreading out load. When a particular RQ has more than 1 active RT task, it is said to be in an "overloaded" state. Once this occurs, the system enters the active balancing mode, where it will try to push the task away, or persuade a different cpu to pull it over. The system will stay in this state until the system falls back below the <= 1 queued RT task per RQ. However, the current implementation suffers from a limitation in the push logic. Once overloaded, all tasks (other than current) on the RQ are analyzed on every push operation, even if it was previously unpushable (due to affinity, etc). Whats more, the operation stops at the first task that is unpushable and will not look at items lower in the queue. This causes two problems: 1) We can have the same tasks analyzed over and over again during each push, which extends out the fast path in the scheduler for no gain. Consider a RQ that has dozens of tasks that are bound to a core. Each one of those tasks will be encountered and skipped for each push operation while they are queued. 2) There may be lower-priority tasks under the unpushable task that could have been successfully pushed, but will never be considered until either the unpushable task is cleared, or a pull operation succeeds. The net result is a potential latency source for mid priority tasks. This patch aims to rectify these two conditions by introducing a new priority sorted list: "pushable_tasks". A task is added to the list each time a task is activated or preempted. It is removed from the list any time it is deactivated, made current, or fails to push. This works because a task only needs to be attempted to push once. After an initial failure to push, the other cpus will eventually try to pull the task when the conditions are proper. This also solves the problem that we don't completely analyze all tasks due to encountering an unpushable tasks. Now every task will have a push attempted (when appropriate). This reduces latency both by shorting the critical section of the rq->lock for certain workloads, and by making sure the algorithm considers all eligible tasks in the system. [ rostedt: added a couple more BUG_ONs ] Signed-off-by: Gregory Haskins Acked-by: Steven Rostedt --- include/linux/init_task.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/init_task.h') diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 23fd8909b9e5..6851225f44a7 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -140,6 +140,7 @@ extern struct group_info init_groups; .nr_cpus_allowed = NR_CPUS, \ }, \ .tasks = LIST_HEAD_INIT(tsk.tasks), \ + .pushable_tasks = PLIST_NODE_INIT(tsk.pushable_tasks, MAX_PRIO), \ .ptraced = LIST_HEAD_INIT(tsk.ptraced), \ .ptrace_entry = LIST_HEAD_INIT(tsk.ptrace_entry), \ .real_parent = &tsk, \ -- cgit v1.2.3 From 5ac9f62267dc92c7735c642a5942d9e6c1190308 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 25 Mar 2009 20:55:00 -0400 Subject: function-graph: add proper initialization for init task Impact: fix to crash going to kexec The init task did not properly initialize the function graph pointers. Altough these pointers are NULL, they can not be assumed to be NULL for the init task, and must still be properly initialize. This usually is not an issue since a problem only arises when a task exits, and the init tasks do not usually exit. But when doing tests with kexec, the init tasks do exit, and the bug appears. This patch properly initializes the init tasks function graph data structures. Reported-and-Tested-by: Yinghai Lu LKML-Reference: Signed-off-by: Steven Rostedt Signed-off-by: Ingo Molnar --- include/linux/init_task.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux/init_task.h') diff --git a/include/linux/init_task.h b/include/linux/init_task.h index e752d973fa21..cada05447bc8 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -5,6 +5,7 @@ #include #include #include +#include #include #include #include @@ -184,6 +185,7 @@ extern struct cred init_cred; INIT_IDS \ INIT_TRACE_IRQFLAGS \ INIT_LOCKDEP \ + INIT_FTRACE_GRAPH \ } -- cgit v1.2.3 From 17a5138d204014b00cb9c1d6e8ff311993041b5c Mon Sep 17 00:00:00 2001 From: Alexey Dobriyan Date: Mon, 13 Apr 2009 14:39:47 -0700 Subject: aio: remove INIT_KIOCTX Unused after 20dcae32439384b6863c626bb3b2a09bed65b33e aka "[PATCH] aio: remove kioctx from mm_struct". Signed-off-by: Alexey Dobriyan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/init_task.h | 13 ------------- 1 file changed, 13 deletions(-) (limited to 'include/linux/init_task.h') diff --git a/include/linux/init_task.h b/include/linux/init_task.h index dcfb93337e9a..d87247d2641f 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -15,19 +15,6 @@ extern struct files_struct init_files; extern struct fs_struct init_fs; -#define INIT_KIOCTX(name, which_mm) \ -{ \ - .users = ATOMIC_INIT(1), \ - .dead = 0, \ - .mm = &which_mm, \ - .user_id = 0, \ - .next = NULL, \ - .wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.wait), \ - .ctx_lock = __SPIN_LOCK_UNLOCKED(name.ctx_lock), \ - .reqs_active = 0U, \ - .max_reqs = ~0U, \ -} - #define INIT_MM(name) \ { \ .mm_rb = RB_ROOT, \ -- cgit v1.2.3