From: Anton Blanchard <anton@samba.org>

- remove min/max yield time, we dont use the values anywhere
- separate shared and dedicated idle loops
- check need_resched again with irqs off to avoid sleeping with pending work
- continually set runlatch off in idle loop, this means we dont need to
  turn the runlatch off on exception exit and suffer that associated
  cost for all exceptions. (A future patch will turn the runlatch on at
  exception entry) 

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 arch/ppc64/kernel/iSeries_setup.c |   84 +++++++++++++++++++++-----------------
 1 files changed, 47 insertions(+), 37 deletions(-)

diff -puN arch/ppc64/kernel/iSeries_setup.c~ppc64-iseries-idle-fixups arch/ppc64/kernel/iSeries_setup.c
--- 25/arch/ppc64/kernel/iSeries_setup.c~ppc64-iseries-idle-fixups	Wed Jul  6 14:10:16 2005
+++ 25-akpm/arch/ppc64/kernel/iSeries_setup.c	Wed Jul  6 14:10:16 2005
@@ -834,9 +834,6 @@ static int __init iSeries_src_init(void)
 
 late_initcall(iSeries_src_init);
 
-static unsigned long maxYieldTime = 0;
-static unsigned long minYieldTime = 0xffffffffffffffffUL;
-
 static inline void process_iSeries_events(void)
 {
 	asm volatile ("li 0,0x5555; sc" : : : "r0", "r3");
@@ -845,7 +842,6 @@ static inline void process_iSeries_event
 static void yield_shared_processor(void)
 {
 	unsigned long tb;
-	unsigned long yieldTime;
 
 	HvCall_setEnabledInterrupts(HvCall_MaskIPI |
 				    HvCall_MaskLpEvent |
@@ -856,13 +852,6 @@ static void yield_shared_processor(void)
 	/* Compute future tb value when yield should expire */
 	HvCall_yieldProcessor(HvCall_YieldTimed, tb+tb_ticks_per_jiffy);
 
-	yieldTime = get_tb() - tb;
-	if (yieldTime > maxYieldTime)
-		maxYieldTime = yieldTime;
-
-	if (yieldTime < minYieldTime)
-		minYieldTime = yieldTime;
-
 	/*
 	 * The decrementer stops during the yield.  Force a fake decrementer
 	 * here and let the timer_interrupt code sort out the actual time.
@@ -871,45 +860,62 @@ static void yield_shared_processor(void)
 	process_iSeries_events();
 }
 
-static int iSeries_idle(void)
+static int iseries_shared_idle(void)
 {
-	struct paca_struct *lpaca;
-	long oldval;
+	while (1) {
+		while (!need_resched() && !hvlpevent_is_pending()) {
+			local_irq_disable();
+			ppc64_runlatch_off();
+
+			/* Recheck with irqs off */
+			if (!need_resched() && !hvlpevent_is_pending())
+				yield_shared_processor();
+
+			HMT_medium();
+			local_irq_enable();
+		}
+
+		ppc64_runlatch_on();
+
+		if (hvlpevent_is_pending())
+			process_iSeries_events();
+
+		schedule();
+	}
 
-	/* ensure iSeries run light will be out when idle */
-	ppc64_runlatch_off();
+	return 0;
+}
 
-	lpaca = get_paca();
+static int iseries_dedicated_idle(void)
+{
+	struct paca_struct *lpaca = get_paca();
+	long oldval;
 
 	while (1) {
-		if (lpaca->lppaca.shared_proc) {
-			if (hvlpevent_is_pending())
-				process_iSeries_events();
-			if (!need_resched())
-				yield_shared_processor();
-		} else {
-			oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED);
+		oldval = test_and_clear_thread_flag(TIF_NEED_RESCHED);
+
+		if (!oldval) {
+			set_thread_flag(TIF_POLLING_NRFLAG);
 
-			if (!oldval) {
-				set_thread_flag(TIF_POLLING_NRFLAG);
+			while (!need_resched()) {
+				ppc64_runlatch_off();
+				HMT_low();
 
-				while (!need_resched()) {
+				if (hvlpevent_is_pending()) {
 					HMT_medium();
-					if (hvlpevent_is_pending())
-						process_iSeries_events();
-					HMT_low();
+					ppc64_runlatch_on();
+					process_iSeries_events();
 				}
-
-				HMT_medium();
-				clear_thread_flag(TIF_POLLING_NRFLAG);
-			} else {
-				set_need_resched();
 			}
+
+			HMT_medium();
+			clear_thread_flag(TIF_POLLING_NRFLAG);
+		} else {
+			set_need_resched();
 		}
 
 		ppc64_runlatch_on();
 		schedule();
-		ppc64_runlatch_off();
 	}
 
 	return 0;
@@ -940,6 +946,10 @@ void __init iSeries_early_setup(void)
 	ppc_md.get_rtc_time = iSeries_get_rtc_time;
 	ppc_md.calibrate_decr = iSeries_calibrate_decr;
 	ppc_md.progress = iSeries_progress;
-	ppc_md.idle_loop = iSeries_idle;
+
+	if (get_paca()->lppaca.shared_proc)
+		ppc_md.idle_loop = iseries_shared_idle;
+	else
+		ppc_md.idle_loop = iseries_dedicated_idle;
 }
 
_