Re: [PATCH] Fix interrupt distribution in ppc970

[Mohan Kumar M <mohan@in.ibm.com>]

I updated the patch with correct tab spacing and removed unnecessary
"else".


In some of the PPC970 based systems, interrupt would be distributed to
offline cpus also even when booted with "maxcpus=1". So check whether
cpu online map and cpu present map are equal or not. If they are equal
default_distrib_server is used as interrupt server otherwise boot cpu
(default_server) used as interrupt server. 

In addition to this, if an interrupt is assigned to a specific cpu (ie
smp affinity) and if that cpu is not online, the earlier code used to
return the default_distrib_server as interrupt server. This patch
introduces an additional paramter to the get_irq function ie
strict_check, based on this parameter, if the cpu is not online either
default_distrib_server or -1 is returned.

Cc: Milton Miller <miltonm@bga.com>,
    Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Mohan Kumar M <mohan@in.ibm.com>
---
 arch/powerpc/platforms/pseries/xics.c |   53 ++++++++++++++++++----------------
 1 file changed, 29 insertions(+), 24 deletions(-)

Index: linux-2.6.21.1/arch/powerpc/platforms/pseries/xics.c
===================================================================
--- linux-2.6.21.1.orig/arch/powerpc/platforms/pseries/xics.c
+++ linux-2.6.21.1/arch/powerpc/platforms/pseries/xics.c
@@ -156,9 +156,9 @@ static inline void lpar_qirr_info(int n_
 
 
 #ifdef CONFIG_SMP
-static int get_irq_server(unsigned int virq)
+static int get_irq_server(unsigned int virq, unsigned int strict_check)
 {
-	unsigned int server;
+	int server;
 	/* For the moment only implement delivery to all cpus or one cpu */
 	cpumask_t cpumask = irq_desc[virq].affinity;
 	cpumask_t tmp = CPU_MASK_NONE;
@@ -166,22 +166,25 @@ static int get_irq_server(unsigned int v
 	if (!distribute_irqs)
 		return default_server;
 
-	if (cpus_equal(cpumask, CPU_MASK_ALL)) {
-		server = default_distrib_server;
-	} else {
+	if (!cpus_equal(cpumask, CPU_MASK_ALL)) {
 		cpus_and(tmp, cpu_online_map, cpumask);
 
-		if (cpus_empty(tmp))
-			server = default_distrib_server;
-		else
-			server = get_hard_smp_processor_id(first_cpu(tmp));
+		server = first_cpu(tmp);
+
+		if (server < NR_CPUS)
+			return get_hard_smp_processor_id(server);
+
+		if (strict_check)
+			return -1;
 	}
 
-	return server;
+	if (cpus_equal(cpu_online_map, cpu_present_map))
+		return default_distrib_server;
 
+	return default_server;
 }
 #else
-static int get_irq_server(unsigned int virq)
+static int get_irq_server(unsigned int virq, unsigned int strict_check)
 {
 	return default_server;
 }
@@ -192,7 +195,7 @@ static void xics_unmask_irq(unsigned int
 {
 	unsigned int irq;
 	int call_status;
-	unsigned int server;
+	int server;
 
 	pr_debug("xics: unmask virq %d\n", virq);
 
@@ -201,7 +204,7 @@ static void xics_unmask_irq(unsigned int
 	if (irq == XICS_IPI || irq == XICS_IRQ_SPURIOUS)
 		return;
 
-	server = get_irq_server(virq);
+	server = get_irq_server(virq, 0);
 
 	call_status = rtas_call(ibm_set_xive, 3, 1, NULL, irq, server,
 				DEFAULT_PRIORITY);
@@ -398,8 +401,7 @@ static void xics_set_affinity(unsigned i
 	unsigned int irq;
 	int status;
 	int xics_status[2];
-	unsigned long newmask;
-	cpumask_t tmp = CPU_MASK_NONE;
+	int irq_server;
 
 	irq = (unsigned int)irq_map[virq].hwirq;
 	if (irq == XICS_IPI || irq == XICS_IRQ_SPURIOUS)
@@ -413,18 +415,21 @@ static void xics_set_affinity(unsigned i
 		return;
 	}
 
-	/* For the moment only implement delivery to all cpus or one cpu */
-	if (cpus_equal(cpumask, CPU_MASK_ALL)) {
-		newmask = default_distrib_server;
-	} else {
-		cpus_and(tmp, cpu_online_map, cpumask);
-		if (cpus_empty(tmp))
-			return;
-		newmask = get_hard_smp_processor_id(first_cpu(tmp));
+	/*
+	 * For the moment only implement delivery to all cpus or one cpu.
+	 * Get current irq_server for the given irq
+	 */
+	irq_server = get_irq_server(irq, 1);
+	if (irq_server == -1) {
+		char cpulist[128];
+		cpulist_scnprintf(cpulist, sizeof(cpulist), cpumask);
+		printk(KERN_WARNING "xics_set_affinity: No online cpus in "
+				"the mask %s for irq %d\n", cpulist, virq);
+		return;
 	}
 
 	status = rtas_call(ibm_set_xive, 3, 1, NULL,
-				irq, newmask, xics_status[1]);
+				irq, irq_server, xics_status[1]);
 
 	if (status) {
 		printk(KERN_ERR "xics_set_affinity: irq=%u ibm,set-xive "