Adjust the interrupt storm handling code to better handle a storm. When

a storm is detected, enter "storming" mode which throttles the interrupt
source such that the handlers are run once every clock tick.  Previously
we allowed a full set of storm_threshold interations through the handler
before going back to sleep.  Also, this currently will intentionally exit
storming mode once a second to see if the storm has passed.

Tested by:	marcus
Discussed with:	bde

1 files changed, 23 insertions, 5 deletions

diff --git a/sys/kern/kern_intr.c b/sys/kern/kern_intr.c
index 6569056..1156883 100644
--- a/sys/kern/kern_intr.c
+++ b/sys/kern/kern_intr.c
@@ -485,7 +485,7 @@ ithread_loop(void *arg)
 	struct intrhand *ih;		/* and our interrupt handler chain */
 	struct thread *td;
 	struct proc *p;
-	int count, warned;
+	int count, warned, storming;
 	
 	td = curthread;
 	p = td->td_proc;
@@ -494,6 +494,7 @@ ithread_loop(void *arg)
 	    ("%s: ithread and proc linkage out of sync", __func__));
 	count = 0;
 	warned = 0;
+	storming = 0;
 
 	/*
 	 * As long as we have interrupts outstanding, go through the
@@ -549,10 +550,26 @@ restart:
 			}
 
 			/*
-			 * If we detect an interrupt storm, pause with the
-			 * source masked until the next hardclock tick.
+			 * Interrupt storm handling:
+			 *
+			 * If this interrupt source is currently storming,
+			 * then throttle it to only fire the handler once
+			 * per clock tick.  Each second we go out of storming
+			 * mode to see if the storm has subsided.
+			 *
+			 * If this interrupt source is not currently
+			 * storming, but the number of back to back
+			 * interrupts exceeds the storm threshold, then
+			 * enter storming mode.
 			 */
-			if (intr_storm_threshold != 0 &&
+			if (storming) {
+				tsleep(&count, td->td_priority, "istorm", 1);
+				if (count > hz) {
+					storming = 0;
+					count = 0;
+				} else
+					count++;
+			} else if (intr_storm_threshold != 0 &&
 			    count >= intr_storm_threshold) {
 				if (!warned) {
 					printf(
@@ -560,7 +577,7 @@ restart:
 					    p->p_comm);
 					warned = 1;
 				}
-				tsleep(&count, td->td_priority, "istorm", 1);
+				storming = 1;
 				count = 0;
 			} else
 				count++;
@@ -580,6 +597,7 @@ restart:
 		if (!ithd->it_need) {
 			TD_SET_IWAIT(td);
 			count = 0;
+			storming = 0;
 			CTR2(KTR_INTR, "%s: pid %d: done", __func__, p->p_pid);
 			mi_switch(SW_VOL, NULL);
 			CTR2(KTR_INTR, "%s: pid %d: resumed", __func__, p->p_pid);