[IA64] Optional method to purge the TLB on SN systems

This patch adds an optional method for purging the TLB on SN IA64 systems.
The change should not affect any non-SN system.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 68 insertions, 0 deletions

diff --git a/arch/ia64/kernel/smp.c b/arch/ia64/kernel/smp.c
index 55ddd809b02..221de380456 100644
--- a/arch/ia64/kernel/smp.c
+++ b/arch/ia64/kernel/smp.c
@@ -50,6 +50,18 @@
 #include <asm/mca.h>
 
 /*
+ * Note: alignment of 4 entries/cacheline was empirically determined
+ * to be a good tradeoff between hot cachelines & spreading the array
+ * across too many cacheline.
+ */
+static struct local_tlb_flush_counts {
+	unsigned int count;
+} __attribute__((__aligned__(32))) local_tlb_flush_counts[NR_CPUS];
+
+static DEFINE_PER_CPU(unsigned int, shadow_flush_counts[NR_CPUS]) ____cacheline_aligned;
+
+
+/*
  * Structure and data for smp_call_function(). This is designed to minimise static memory
  * requirements. It also looks cleaner.
  */
@@ -248,6 +260,62 @@ smp_send_reschedule (int cpu)
 	platform_send_ipi(cpu, IA64_IPI_RESCHEDULE, IA64_IPI_DM_INT, 0);
 }
 
+/*
+ * Called with preeemption disabled.
+ */
+static void
+smp_send_local_flush_tlb (int cpu)
+{
+	platform_send_ipi(cpu, IA64_IPI_LOCAL_TLB_FLUSH, IA64_IPI_DM_INT, 0);
+}
+
+void
+smp_local_flush_tlb(void)
+{
+	/*
+	 * Use atomic ops. Otherwise, the load/increment/store sequence from
+	 * a "++" operation can have the line stolen between the load & store.
+	 * The overhead of the atomic op in negligible in this case & offers
+	 * significant benefit for the brief periods where lots of cpus
+	 * are simultaneously flushing TLBs.
+	 */
+	ia64_fetchadd(1, &local_tlb_flush_counts[smp_processor_id()].count, acq);
+	local_flush_tlb_all();
+}
+
+#define FLUSH_DELAY	5 /* Usec backoff to eliminate excessive cacheline bouncing */
+
+void
+smp_flush_tlb_cpumask(cpumask_t xcpumask)
+{
+	unsigned int *counts = __ia64_per_cpu_var(shadow_flush_counts);
+	cpumask_t cpumask = xcpumask;
+	int mycpu, cpu, flush_mycpu = 0;
+
+	preempt_disable();
+	mycpu = smp_processor_id();
+
+	for_each_cpu_mask(cpu, cpumask)
+		counts[cpu] = local_tlb_flush_counts[cpu].count;
+
+	mb();
+	for_each_cpu_mask(cpu, cpumask) {
+		if (cpu == mycpu)
+			flush_mycpu = 1;
+		else
+			smp_send_local_flush_tlb(cpu);
+	}
+
+	if (flush_mycpu)
+		smp_local_flush_tlb();
+
+	for_each_cpu_mask(cpu, cpumask)
+		while(counts[cpu] == local_tlb_flush_counts[cpu].count)
+			udelay(FLUSH_DELAY);
+
+	preempt_enable();
+}
+
 void
 smp_flush_tlb_all (void)
 {