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From: Alexander Motin <mav@FreeBSD.org>
Date: Fri, 10 Sep 2010 13:24:47 +0000 (UTC)
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Subject: svn commit: r212416 - head/sys/kern
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Author: mav
Date: Fri Sep 10 13:24:47 2010
New Revision: 212416
URL: http://svn.freebsd.org/changeset/base/212416

Log:
  Do not IPI CPU that is already spinning for load. It doubles effect of
  spining (comparing to MWAIT) on some heavly switching test loads.

Modified:
  head/sys/kern/sched_ule.c

Modified: head/sys/kern/sched_ule.c
==============================================================================
--- head/sys/kern/sched_ule.c	Fri Sep 10 12:55:36 2010	(r212415)
+++ head/sys/kern/sched_ule.c	Fri Sep 10 13:24:47 2010	(r212416)
@@ -196,7 +196,7 @@ static int preempt_thresh = 0;
 #endif
 static int static_boost = PRI_MIN_TIMESHARE;
 static int sched_idlespins = 10000;
-static int sched_idlespinthresh = 4;
+static int sched_idlespinthresh = 64;
 
 /*
  * tdq - per processor runqs and statistics.  All fields are protected by the
@@ -208,6 +208,7 @@ struct tdq {
 	struct mtx	tdq_lock;		/* run queue lock. */
 	struct cpu_group *tdq_cg;		/* Pointer to cpu topology. */
 	volatile int	tdq_load;		/* Aggregate load. */
+	volatile int	tdq_cpu_idle;		/* cpu_idle() is active. */
 	int		tdq_sysload;		/* For loadavg, !ITHD load. */
 	int		tdq_transferable;	/* Transferable thread count. */
 	short		tdq_switchcnt;		/* Switches this tick. */
@@ -966,7 +967,7 @@ tdq_notify(struct tdq *tdq, struct threa
 		 * If the MD code has an idle wakeup routine try that before
 		 * falling back to IPI.
 		 */
-		if (cpu_idle_wakeup(cpu))
+		if (!tdq->tdq_cpu_idle || cpu_idle_wakeup(cpu))
 			return;
 	}
 	tdq->tdq_ipipending = 1;
@@ -2545,8 +2546,14 @@ sched_idletd(void *dummy)
 			}
 		}
 		switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
-		if (tdq->tdq_load == 0)
-			cpu_idle(switchcnt > 1);
+		if (tdq->tdq_load == 0) {
+			tdq->tdq_cpu_idle = 1;
+			if (tdq->tdq_load == 0) {
+				cpu_idle(switchcnt > sched_idlespinthresh);
+				tdq->tdq_switchcnt++;
+			}
+			tdq->tdq_cpu_idle = 0;
+		}
 		if (tdq->tdq_load) {
 			thread_lock(td);
 			mi_switch(SW_VOL | SWT_IDLE, NULL);