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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 /arch/sh64
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 'arch/sh64')
-rw-r--r--arch/sh64/kernel/process.c14
1 files changed, 3 insertions, 11 deletions
diff --git a/arch/sh64/kernel/process.c b/arch/sh64/kernel/process.c
index 0c09537449b3..b95d04141855 100644
--- a/arch/sh64/kernel/process.c
+++ b/arch/sh64/kernel/process.c
@@ -307,23 +307,19 @@ __setup("hlt", hlt_setup);
307 307
308static inline void hlt(void) 308static inline void hlt(void)
309{ 309{
310 if (hlt_counter)
311 return;
312
313 __asm__ __volatile__ ("sleep" : : : "memory"); 310 __asm__ __volatile__ ("sleep" : : : "memory");
314} 311}
315 312
316/* 313/*
317 * The idle loop on a uniprocessor SH.. 314 * The idle loop on a uniprocessor SH..
318 */ 315 */
319void default_idle(void) 316void cpu_idle(void)
320{ 317{
321 /* endless idle loop with no priority at all */ 318 /* endless idle loop with no priority at all */
322 while (1) { 319 while (1) {
323 if (hlt_counter) { 320 if (hlt_counter) {
324 while (1) 321 while (!need_resched())
325 if (need_resched()) 322 cpu_relax();
326 break;
327 } else { 323 } else {
328 local_irq_disable(); 324 local_irq_disable();
329 while (!need_resched()) { 325 while (!need_resched()) {
@@ -338,11 +334,7 @@ void default_idle(void)
338 schedule(); 334 schedule();
339 preempt_disable(); 335 preempt_disable();
340 } 336 }
341}
342 337
343void cpu_idle(void)
344{
345 default_idle();
346} 338}
347 339
348void machine_restart(char * __unused) 340void machine_restart(char * __unused)