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authorNick Piggin <nickpiggin@yahoo.com.au>2005-11-08 21:39:04 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2005-11-09 07:56:33 -0800
commit64c7c8f88559624abdbe12b5da6502e8879f8d28 (patch)
tree02f85a35ddd0f24dec70e5d6ecd61073578fd8d6 /arch/powerpc
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/powerpc')
-rw-r--r--arch/powerpc/platforms/iseries/setup.c10
-rw-r--r--arch/powerpc/platforms/pseries/setup.c12
2 files changed, 6 insertions, 16 deletions
diff --git a/arch/powerpc/platforms/iseries/setup.c b/arch/powerpc/platforms/iseries/setup.c
index 0130f2619da..7f8f0cda6a7 100644
--- a/arch/powerpc/platforms/iseries/setup.c
+++ b/arch/powerpc/platforms/iseries/setup.c
@@ -703,13 +703,10 @@ static void iseries_shared_idle(void)
static void iseries_dedicated_idle(void)
{
long oldval;
+ set_thread_flag(TIF_POLLING_NRFLAG);
while (1) {
- oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED);
-
- if (!oldval) {
- set_thread_flag(TIF_POLLING_NRFLAG);
-
+ if (!need_resched()) {
while (!need_resched()) {
ppc64_runlatch_off();
HMT_low();
@@ -722,9 +719,6 @@ static void iseries_dedicated_idle(void)
}
HMT_medium();
- clear_thread_flag(TIF_POLLING_NRFLAG);
- } else {
- set_need_resched();
}
ppc64_runlatch_on();
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 4854f5eb5c3..a093a0d4dd6 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -469,6 +469,7 @@ static inline void dedicated_idle_sleep(unsigned int cpu)
* more.
*/
clear_thread_flag(TIF_POLLING_NRFLAG);
+ smp_mb__after_clear_bit();
/*
* SMT dynamic mode. Cede will result in this thread going
@@ -481,6 +482,7 @@ static inline void dedicated_idle_sleep(unsigned int cpu)
cede_processor();
else
local_irq_enable();
+ set_thread_flag(TIF_POLLING_NRFLAG);
} else {
/*
* Give the HV an opportunity at the processor, since we are
@@ -492,11 +494,11 @@ static inline void dedicated_idle_sleep(unsigned int cpu)
static void pseries_dedicated_idle(void)
{
- long oldval;
struct paca_struct *lpaca = get_paca();
unsigned int cpu = smp_processor_id();
unsigned long start_snooze;
unsigned long *smt_snooze_delay = &__get_cpu_var(smt_snooze_delay);
+ set_thread_flag(TIF_POLLING_NRFLAG);
while (1) {
/*
@@ -505,10 +507,7 @@ static void pseries_dedicated_idle(void)
*/
lpaca->lppaca.idle = 1;
- oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED);
- if (!oldval) {
- set_thread_flag(TIF_POLLING_NRFLAG);
-
+ if (!need_resched()) {
start_snooze = __get_tb() +
*smt_snooze_delay * tb_ticks_per_usec;
@@ -531,9 +530,6 @@ static void pseries_dedicated_idle(void)
}
HMT_medium();
- clear_thread_flag(TIF_POLLING_NRFLAG);
- } else {
- set_need_resched();
}
lpaca->lppaca.idle = 0;