[ovs-dev] [PATCH 1/1] netdev-dpdk: Fixed netdev_dpdk structure alignment

Eelco Chaudron echaudro at redhat.com
Wed Apr 25 15:48:23 UTC 2018


Currently, the code tells us we have 4 pad bytes left in cacheline0
while actually we are 8 bytes short:

struct netdev_dpdk {
	union {
		OVS_CACHE_LINE_MARKER cacheline0;        /*           1 */
		struct {
			dpdk_port_t port_id;             /*     0     2 */
			_Bool      attached;             /*     2     1 */
			struct eth_addr hwaddr;          /*     4     6 */
			int        mtu;                  /*    12     4 */
			int        socket_id;            /*    16     4 */
			int        buf_size;             /*    20     4 */
			int        max_packet_len;       /*    24     4 */
			enum dpdk_dev_type type;         /*    28     4 */
			enum netdev_flags flags;         /*    32     4 */
			char *     devargs;              /*    40     8 */
			struct dpdk_tx_queue * tx_q;     /*    48     8 */
			struct rte_eth_link link;        /*    56     8 */
			int        link_reset_cnt;       /*    64     4 */
		};                                       /*          72 */
		uint8_t            pad9[128];            /*         128 */
	};                                               /*     0   128 */
	/* --- cacheline 2 boundary (128 bytes) --- */

Re-located one member, link_reset_cnt, and now it's one cache line:

struct netdev_dpdk {
	union {
		OVS_CACHE_LINE_MARKER cacheline0;        /*           1 */
		struct {
			dpdk_port_t port_id;             /*     0     2 */
			_Bool      attached;             /*     2     1 */
			struct eth_addr hwaddr;          /*     4     6 */
			int        mtu;                  /*    12     4 */
			int        socket_id;            /*    16     4 */
			int        buf_size;             /*    20     4 */
			int        max_packet_len;       /*    24     4 */
			enum dpdk_dev_type type;         /*    28     4 */
			enum netdev_flags flags;         /*    32     4 */
			int        link_reset_cnt;       /*    36     4 */
			char *     devargs;              /*    40     8 */
			struct dpdk_tx_queue * tx_q;     /*    48     8 */
			struct rte_eth_link link;        /*    56     8 */
		};                                       /*          64 */
		uint8_t            pad9[64];             /*          64 */
	};                                               /*     0    64 */
	/* --- cacheline 1 boundary (64 bytes) --- */

Signed-off-by: Eelco Chaudron <echaudro at redhat.com>
---
 lib/netdev-dpdk.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
index ee39cbe4a..b14140571 100644
--- a/lib/netdev-dpdk.c
+++ b/lib/netdev-dpdk.c
@@ -363,11 +363,10 @@ struct netdev_dpdk {
         int max_packet_len;
         enum dpdk_dev_type type;
         enum netdev_flags flags;
+        int link_reset_cnt;
         char *devargs;  /* Device arguments for dpdk ports */
         struct dpdk_tx_queue *tx_q;
         struct rte_eth_link link;
-        int link_reset_cnt;
-        /* 4 pad bytes here. */
     );
 
     PADDED_MEMBERS_CACHELINE_MARKER(CACHE_LINE_SIZE, cacheline1,
-- 
2.14.3



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