From: Keir Fraser <keir.fraser@citrix.com>
Date: Wed, 3 Feb 2010 09:30:46 +0000 (+0000)
Subject: xen/evtchn: MAke round-robin scan fairer by snapshotting each l2 word
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=99982b91aaf6c9b1e3a8b369102323112f96faa8;p=legacy%2Flinux-2.6.18-xen.git

xen/evtchn: MAke round-robin scan fairer by snapshotting each l2 word
once only (except for starting l2 word, which we scan in two parts).

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
---

diff --git a/drivers/xen/core/evtchn.c b/drivers/xen/core/evtchn.c
index c395ce52..469f078a 100644
--- a/drivers/xen/core/evtchn.c
+++ b/drivers/xen/core/evtchn.c
@@ -238,7 +238,7 @@ asmlinkage void evtchn_do_upcall(struct pt_regs *regs)
 {
 	unsigned long       l1, l2;
 	unsigned long       masked_l1, masked_l2;
-	unsigned int        l1i, l2i, port, count;
+	unsigned int        l1i, l2i, start_l1i, start_l2i, port, count, i;
 	int                 irq;
 	unsigned int        cpu = smp_processor_id();
 	shared_info_t      *s = HYPERVISOR_shared_info;
@@ -261,10 +261,10 @@ asmlinkage void evtchn_do_upcall(struct pt_regs *regs)
 #endif
 		l1 = xchg(&vcpu_info->evtchn_pending_sel, 0);
 
-		l1i = per_cpu(current_l1i, cpu);
-		l2i = per_cpu(current_l2i, cpu);
+		start_l1i = l1i = per_cpu(current_l1i, cpu);
+		start_l2i = per_cpu(current_l2i, cpu);
 
-		while (l1 != 0) {
+		for (i = 0; l1 != 0; i++) {
 			masked_l1 = l1 & ((~0UL) << l1i);
 			/* If we masked out all events, wrap to beginning. */
 			if (masked_l1 == 0) {
@@ -273,8 +273,19 @@ asmlinkage void evtchn_do_upcall(struct pt_regs *regs)
 			}
 			l1i = __ffs(masked_l1);
 
+			l2 = active_evtchns(cpu, s, l1i);
+			l2i = 0; /* usually scan entire word from start */
+			if (l1i == start_l1i) {
+				/* We scan the starting word in two parts. */
+				if (i == 0)
+					/* 1st time: start in the middle */
+					l2i = start_l2i;
+				else
+					/* 2nd time: mask bits done already */
+					l2 &= (1ul << start_l2i) - 1;
+			}
+
 			do {
-				l2 = active_evtchns(cpu, s, l1i);
 				masked_l2 = l2 & ((~0UL) << l2i);
 				if (masked_l2 == 0)
 					break;
@@ -296,9 +307,8 @@ asmlinkage void evtchn_do_upcall(struct pt_regs *regs)
 
 			} while (l2i != 0);
 
-			l2 = active_evtchns(cpu, s, l1i);
-			/* If we handled all ports, clear the selector bit. */
-			if (l2 == 0)
+			/* Scan start_l1i twice; all others once. */
+			if ((l1i != start_l1i) || (i != 0))
 				l1 &= ~(1UL << l1i);
 
 			l1i = (l1i + 1) % BITS_PER_LONG;