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| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2010-11-13 19:32:29 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2010-11-18 13:27:46 +0100 |
| commit | 48c5ccae88dcd989d9de507e8510313c6cbd352b (patch) | |
| tree | 06fe8ce2ac28e9f5844de8bc32ecbef97e40d68b /kernel/cpu.c | |
| parent | 92fd4d4d67b945c0766416284d4ab236b31542c4 (diff) | |
| download | linux-48c5ccae88dcd989d9de507e8510313c6cbd352b.tar.bz2 | |
sched: Simplify cpu-hot-unplug task migration
While discussing the need for sched_idle_next(), Oleg remarked that
since try_to_wake_up() ensures sleeping tasks will end up running on a
sane cpu, we can do away with migrate_live_tasks().
If we then extend the existing hack of migrating current from
CPU_DYING to migrating the full rq worth of tasks from CPU_DYING, the
need for the sched_idle_next() abomination disappears as well, since
idle will be the only possible thread left after the migration thread
stops.
This greatly simplifies the hot-unplug task migration path, as can be
seen from the resulting code reduction (and about half the new lines
are comments).
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1289851597.2109.547.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/cpu.c')
| -rw-r--r-- | kernel/cpu.c | 16 |
1 files changed, 6 insertions, 10 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c index f6e726f18491..8615aa65d927 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -189,7 +189,6 @@ static inline void check_for_tasks(int cpu) } struct take_cpu_down_param { - struct task_struct *caller; unsigned long mod; void *hcpu; }; @@ -208,11 +207,6 @@ static int __ref take_cpu_down(void *_param) cpu_notify(CPU_DYING | param->mod, param->hcpu); - if (task_cpu(param->caller) == cpu) - move_task_off_dead_cpu(cpu, param->caller); - /* Force idle task to run as soon as we yield: it should - immediately notice cpu is offline and die quickly. */ - sched_idle_next(); return 0; } @@ -223,7 +217,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) void *hcpu = (void *)(long)cpu; unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0; struct take_cpu_down_param tcd_param = { - .caller = current, .mod = mod, .hcpu = hcpu, }; @@ -253,9 +246,12 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) } BUG_ON(cpu_online(cpu)); - /* Wait for it to sleep (leaving idle task). */ - while (!idle_cpu(cpu)) - yield(); + /* + * The migration_call() CPU_DYING callback will have removed all + * runnable tasks from the cpu, there's only the idle task left now + * that the migration thread is done doing the stop_machine thing. + */ + BUG_ON(!idle_cpu(cpu)); /* This actually kills the CPU. */ __cpu_die(cpu); |