From: Eric Dumazet <eduma...@google.com>
sd->input_queue_head is incremented for each processed packet
in process_backlog(), and read from other cpus performing
Out Of Order avoidance in get_rps_cpu()
Moving this field in a separate cache line keeps it mostly
hot for the cpu in process_backlog(), as other cpus will
only read it.
In a stress test, process_backlog() was consuming 6.80 % of cpu cycles,
and the patch reduced the cost to 0.65 %
Signed-off-by: Eric Dumazet <eduma...@google.com>
---
include/linux/netdevice.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 18d8394f2e5d..934ca866562d 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2747,11 +2747,15 @@ struct softnet_data {
struct sk_buff *completion_queue;
#ifdef CONFIG_RPS
- /* Elements below can be accessed between CPUs for RPS */
+ /* input_queue_head should be written by cpu owning this struct,
+ * and only read by other cpus. Worth using a cache line.
+ */
+ unsigned int input_queue_head ____cacheline_aligned_in_smp;
+
+ /* Elements below can be accessed between CPUs for RPS/RFS */
struct call_single_data csd ____cacheline_aligned_in_smp;
struct softnet_data *rps_ipi_next;
unsigned int cpu;
- unsigned int input_queue_head;
unsigned int input_queue_tail;
#endif
unsigned int dropped;
