[PATCH v2] nohz: prevent tilegx network driver interrupts

[Chris Metcalf <cmetcalf@ezchip.com>]

Normally the tilegx networking shim sends irqs to all the cores
to distribute the load of processing incoming-packet interrupts,
so that you can get to multiple Gb's of traffic inbound.

However, in nohz_full mode we don't want to interrupt the
nohz_full cores by default, so we limit the set of cores we use
to only the online housekeeping cores.

To make client code easier to read, we introduce a new nohz_full
accessor, housekeeping_cpumask(), which returns a pointer to the
housekeeping_mask if nohz_full is enabled, and otherwise returns
the cpu_possible_mask.

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
---
 drivers/net/ethernet/tile/tilegx.c | 4 +++-
 include/linux/tick.h               | 9 +++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/tile/tilegx.c b/drivers/net/ethernet/tile/tilegx.c
index a3f7610002aa..0a15acc075b3 100644
--- a/drivers/net/ethernet/tile/tilegx.c
+++ b/drivers/net/ethernet/tile/tilegx.c
@@ -40,6 +40,7 @@
 #include <linux/tcp.h>
 #include <linux/net_tstamp.h>
 #include <linux/ptp_clock_kernel.h>
+#include <linux/tick.h>
 
 #include <asm/checksum.h>
 #include <asm/homecache.h>
@@ -2273,7 +2274,8 @@ static int __init tile_net_init_module(void)
 		tile_net_dev_init(name, mac);
 
 	if (!network_cpus_init())
-		network_cpus_map = *cpu_online_mask;
+		cpumask_and(&network_cpus_map, housekeeping_cpumask(),
+			    cpu_online_mask);
 
 	return 0;
 }
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 3741ba1a652c..d3b00f0b2221 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -160,6 +160,15 @@ static inline void tick_nohz_full_kick_all(void) { }
 static inline void __tick_nohz_task_switch(struct task_struct *tsk) { }
 #endif
 
+static inline const struct cpumask *housekeeping_cpumask(void)
+{
+#ifdef CONFIG_NO_HZ_FULL
+	if (tick_nohz_full_enabled())
+		return housekeeping_mask;
+#endif
+	return cpu_possible_mask;
+}
+
 static inline bool is_housekeeping_cpu(int cpu)
 {
 #ifdef CONFIG_NO_HZ_FULL
-- 
2.1.2