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authorNick Piggin <nickpiggin@yahoo.com.au>2005-11-09 00:39:04 -0500
committerLinus Torvalds <torvalds@g5.osdl.org>2005-11-09 10:56:33 -0500
commit64c7c8f88559624abdbe12b5da6502e8879f8d28 (patch)
tree02f85a35ddd0f24dec70e5d6ecd61073578fd8d6 /drivers/acpi
parent5bfb5d690f36d316a5f3b4f7775fda996faa6b12 (diff)
[PATCH] sched: resched and cpu_idle rework
Make some changes to the NEED_RESCHED and POLLING_NRFLAG to reduce confusion, and make their semantics rigid. Improves efficiency of resched_task and some cpu_idle routines. * In resched_task: - TIF_NEED_RESCHED is only cleared with the task's runqueue lock held, and as we hold it during resched_task, then there is no need for an atomic test and set there. The only other time this should be set is when the task's quantum expires, in the timer interrupt - this is protected against because the rq lock is irq-safe. - If TIF_NEED_RESCHED is set, then we don't need to do anything. It won't get unset until the task get's schedule()d off. - If we are running on the same CPU as the task we resched, then set TIF_NEED_RESCHED and no further action is required. - If we are running on another CPU, and TIF_POLLING_NRFLAG is *not* set after TIF_NEED_RESCHED has been set, then we need to send an IPI. Using these rules, we are able to remove the test and set operation in resched_task, and make clear the previously vague semantics of POLLING_NRFLAG. * In idle routines: - Enter cpu_idle with preempt disabled. When the need_resched() condition becomes true, explicitly call schedule(). This makes things a bit clearer (IMO), but haven't updated all architectures yet. - Many do a test and clear of TIF_NEED_RESCHED for some reason. According to the resched_task rules, this isn't needed (and actually breaks the assumption that TIF_NEED_RESCHED is only cleared with the runqueue lock held). So remove that. Generally one less locked memory op when switching to the idle thread. - Many idle routines clear TIF_POLLING_NRFLAG, and only set it in the inner most polling idle loops. The above resched_task semantics allow it to be set until before the last time need_resched() is checked before going into a halt requiring interrupt wakeup. Many idle routines simply never enter such a halt, and so POLLING_NRFLAG can be always left set, completely eliminating resched IPIs when rescheduling the idle task. POLLING_NRFLAG width can be increased, to reduce the chance of resched IPIs. Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Ingo Molnar <mingo@elte.hu> Cc: Con Kolivas <kernel@kolivas.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'drivers/acpi')
-rw-r--r--drivers/acpi/processor_idle.c37
1 files changed, 23 insertions, 14 deletions
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 161db4acfb91..573b6a97bb1f 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -167,6 +167,19 @@ acpi_processor_power_activate(struct acpi_processor *pr,
167 return; 167 return;
168} 168}
169 169
170static void acpi_safe_halt(void)
171{
172 int polling = test_thread_flag(TIF_POLLING_NRFLAG);
173 if (polling) {
174 clear_thread_flag(TIF_POLLING_NRFLAG);
175 smp_mb__after_clear_bit();
176 }
177 if (!need_resched())
178 safe_halt();
179 if (polling)
180 set_thread_flag(TIF_POLLING_NRFLAG);
181}
182
170static atomic_t c3_cpu_count; 183static atomic_t c3_cpu_count;
171 184
172static void acpi_processor_idle(void) 185static void acpi_processor_idle(void)
@@ -177,7 +190,7 @@ static void acpi_processor_idle(void)
177 int sleep_ticks = 0; 190 int sleep_ticks = 0;
178 u32 t1, t2 = 0; 191 u32 t1, t2 = 0;
179 192
180 pr = processors[raw_smp_processor_id()]; 193 pr = processors[smp_processor_id()];
181 if (!pr) 194 if (!pr)
182 return; 195 return;
183 196
@@ -197,8 +210,13 @@ static void acpi_processor_idle(void)
197 } 210 }
198 211
199 cx = pr->power.state; 212 cx = pr->power.state;
200 if (!cx) 213 if (!cx) {
201 goto easy_out; 214 if (pm_idle_save)
215 pm_idle_save();
216 else
217 acpi_safe_halt();
218 return;
219 }
202 220
203 /* 221 /*
204 * Check BM Activity 222 * Check BM Activity
@@ -278,7 +296,8 @@ static void acpi_processor_idle(void)
278 if (pm_idle_save) 296 if (pm_idle_save)
279 pm_idle_save(); 297 pm_idle_save();
280 else 298 else
281 safe_halt(); 299 acpi_safe_halt();
300
282 /* 301 /*
283 * TBD: Can't get time duration while in C1, as resumes 302 * TBD: Can't get time duration while in C1, as resumes
284 * go to an ISR rather than here. Need to instrument 303 * go to an ISR rather than here. Need to instrument
@@ -414,16 +433,6 @@ static void acpi_processor_idle(void)
414 */ 433 */
415 if (next_state != pr->power.state) 434 if (next_state != pr->power.state)
416 acpi_processor_power_activate(pr, next_state); 435 acpi_processor_power_activate(pr, next_state);
417
418 return;
419
420 easy_out:
421 /* do C1 instead of busy loop */
422 if (pm_idle_save)
423 pm_idle_save();
424 else
425 safe_halt();
426 return;
427} 436}
428 437
429static int acpi_processor_set_power_policy(struct acpi_processor *pr) 438static int acpi_processor_set_power_policy(struct acpi_processor *pr)