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net-rfs: fix false sharing accessing sd->input_queue_head

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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 <edumazet@google.com>
Acked-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2016-04-26 15:30:07 -07:00 committed by David S. Miller
parent 35ef7d689d
commit 501e7ef569
1 changed files with 6 additions and 2 deletions
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8
include/linux/netdevice.h
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@ -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;