diff options
author | Tejun Heo <tj@kernel.org> | 2010-05-06 12:49:21 -0400 |
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committer | Tejun Heo <tj@kernel.org> | 2010-05-06 12:49:21 -0400 |
commit | 969c79215a35b06e5e3efe69b9412f858df7856c (patch) | |
tree | 4256378687c8bc2011ec35a3e28bc3b6473e912c /Documentation/RCU | |
parent | 3fc1f1e27a5b807791d72e5d992aa33b668a6626 (diff) |
sched: replace migration_thread with cpu_stop
Currently migration_thread is serving three purposes - migration
pusher, context to execute active_load_balance() and forced context
switcher for expedited RCU synchronize_sched. All three roles are
hardcoded into migration_thread() and determining which job is
scheduled is slightly messy.
This patch kills migration_thread and replaces all three uses with
cpu_stop. The three different roles of migration_thread() are
splitted into three separate cpu_stop callbacks -
migration_cpu_stop(), active_load_balance_cpu_stop() and
synchronize_sched_expedited_cpu_stop() - and each use case now simply
asks cpu_stop to execute the callback as necessary.
synchronize_sched_expedited() was implemented with private
preallocated resources and custom multi-cpu queueing and waiting
logic, both of which are provided by cpu_stop.
synchronize_sched_expedited_count is made atomic and all other shared
resources along with the mutex are dropped.
synchronize_sched_expedited() also implemented a check to detect cases
where not all the callback got executed on their assigned cpus and
fall back to synchronize_sched(). If called with cpu hotplug blocked,
cpu_stop already guarantees that and the condition cannot happen;
otherwise, stop_machine() would break. However, this patch preserves
the paranoid check using a cpumask to record on which cpus the stopper
ran so that it can serve as a bisection point if something actually
goes wrong theree.
Because the internal execution state is no longer visible,
rcu_expedited_torture_stats() is removed.
This patch also renames cpu_stop threads to from "stopper/%d" to
"migration/%d". The names of these threads ultimately don't matter
and there's no reason to make unnecessary userland visible changes.
With this patch applied, stop_machine() and sched now share the same
resources. stop_machine() is faster without wasting any resources and
sched migration users are much cleaner.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Josh Triplett <josh@freedesktop.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r-- | Documentation/RCU/torture.txt | 10 |
1 files changed, 0 insertions, 10 deletions
diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt index 0e50bc2aa1e2..5d9016795fd8 100644 --- a/Documentation/RCU/torture.txt +++ b/Documentation/RCU/torture.txt | |||
@@ -182,16 +182,6 @@ Similarly, sched_expedited RCU provides the following: | |||
182 | sched_expedited-torture: Reader Pipe: 12660320201 95875 0 0 0 0 0 0 0 0 0 | 182 | sched_expedited-torture: Reader Pipe: 12660320201 95875 0 0 0 0 0 0 0 0 0 |
183 | sched_expedited-torture: Reader Batch: 12660424885 0 0 0 0 0 0 0 0 0 0 | 183 | sched_expedited-torture: Reader Batch: 12660424885 0 0 0 0 0 0 0 0 0 0 |
184 | sched_expedited-torture: Free-Block Circulation: 1090795 1090795 1090794 1090793 1090792 1090791 1090790 1090789 1090788 1090787 0 | 184 | sched_expedited-torture: Free-Block Circulation: 1090795 1090795 1090794 1090793 1090792 1090791 1090790 1090789 1090788 1090787 0 |
185 | state: -1 / 0:0 3:0 4:0 | ||
186 | |||
187 | As before, the first four lines are similar to those for RCU. | ||
188 | The last line shows the task-migration state. The first number is | ||
189 | -1 if synchronize_sched_expedited() is idle, -2 if in the process of | ||
190 | posting wakeups to the migration kthreads, and N when waiting on CPU N. | ||
191 | Each of the colon-separated fields following the "/" is a CPU:state pair. | ||
192 | Valid states are "0" for idle, "1" for waiting for quiescent state, | ||
193 | "2" for passed through quiescent state, and "3" when a race with a | ||
194 | CPU-hotplug event forces use of the synchronize_sched() primitive. | ||
195 | 185 | ||
196 | 186 | ||
197 | USAGE | 187 | USAGE |