One of the [many] nice properties of the traditional Don Becker drivers
has been that often the driver-private structures are arranged such that
the structure is broken up on cacheline boundaries. The RX thread has
a cacheline, the TX thread has a cacheline, etc. Jes Sorensen also
independently, in his review of 8139cp.c, suggested that the
driver-private struct be update with attention to cacheline boundaries.
Early next year, I would like to start cleaning up some of the net
drivers along these lines (no pun intended). To make it easier for
vendors and random coders to cacheline-align struct members, I would
like to make more explicit these cacheline boundaries, in a manner that
is portable between 32-bit and 64-bit systems.
I attach a sample implementation, and request feedback on this approach.
The general idea is to make implementing this sort of concept "harder
to screw up."
===== drivers/net/tg3.c 1.41 vs edited =====
--- 1.41/drivers/net/tg3.c Wed Nov 20 00:49:23 2002
+++ edited/drivers/net/tg3.c Sat Dec 7 17:12:38 2002
@@ -25,6 +25,7 @@
#include <linux/if_vlan.h>
#include <linux/ip.h>
#include <linux/tcp.h>
+#include <linux/cache.h>
#include <asm/system.h>
#include <asm/io.h>
===== drivers/net/tg3.h 1.19 vs edited =====
--- 1.19/drivers/net/tg3.h Mon Nov 11 05:27:52 2002
+++ edited/drivers/net/tg3.h Sat Dec 7 17:20:25 2002
@@ -1741,17 +1741,66 @@
* necessary for acquisition of 'tx_lock'.
*/
spinlock_t lock;
- spinlock_t tx_lock;
+ spinlock_t indirect_lock;
+
+ unsigned long regs;
+ struct net_device *dev;
+ struct pci_dev *pdev;
+
+ struct tg3_hw_status *hw_status;
+ dma_addr_t status_mapping;
+
+ u32 msg_enable;
+
+ /* end "general, frequently-used members" cacheline section */
+ ALIGNED_PAD(_pad1_)
u32 tx_prod;
u32 tx_cons;
+ u32 tx_pending;
+
+ spinlock_t tx_lock;
+
+ /* TX descs are only used if TG3_FLAG_HOST_TXDS is set. */
+ struct tg3_tx_buffer_desc *tx_ring;
+ struct tx_ring_info *tx_buffers;
+ dma_addr_t tx_desc_mapping;
+
+ /* end "tx thread" cacheline section */
+ ALIGNED_PAD(_pad2_)
+
u32 rx_rcb_ptr;
u32 rx_std_ptr;
u32 rx_jumbo_ptr;
#if TG3_MINI_RING_WORKS
u32 rx_mini_ptr;
#endif
- spinlock_t indirect_lock;
+ u32 rx_pending;
+#if TG3_MINI_RING_WORKS
+ u32 rx_mini_pending;
+#endif
+ u32 rx_jumbo_pending;
+#if TG3_VLAN_TAG_USED
+ struct vlan_group *vlgrp;
+#endif
+
+ struct tg3_rx_buffer_desc *rx_std;
+ struct ring_info *rx_std_buffers;
+ dma_addr_t rx_std_mapping;
+#if TG3_MINI_RING_WORKS
+ struct tg3_rx_buffer_desc *rx_mini;
+ struct ring_info *rx_mini_buffers;
+ dma_addr_t rx_mini_mapping;
+#endif
+ struct tg3_rx_buffer_desc *rx_jumbo;
+ struct ring_info *rx_jumbo_buffers;
+ dma_addr_t rx_jumbo_mapping;
+
+ struct tg3_rx_buffer_desc *rx_rcb;
+ dma_addr_t rx_rcb_mapping;
+
+ /* end "rx thread" cacheline section */
+ ALIGNED_PAD(_pad3_)
struct net_device_stats net_stats;
struct net_device_stats net_stats_prev;
@@ -1791,8 +1840,6 @@
#define TG3_FLAG_SPLIT_MODE 0x40000000
#define TG3_FLAG_INIT_COMPLETE 0x80000000
- u32 msg_enable;
-
u32 split_mode_max_reqs;
#define SPLIT_MODE_5704_MAX_REQ 3
@@ -1806,13 +1853,6 @@
struct tg3_link_config link_config;
struct tg3_bufmgr_config bufmgr_config;
- u32 rx_pending;
-#if TG3_MINI_RING_WORKS
- u32 rx_mini_pending;
-#endif
- u32 rx_jumbo_pending;
- u32 tx_pending;
-
/* cache h/w values, often passed straight to h/w */
u32 rx_mode;
u32 tx_mode;
@@ -1865,38 +1905,10 @@
(X) == PHY_ID_BCM5703 || (X) == PHY_ID_BCM5704 || \
(X) == PHY_ID_BCM8002 || (X) == PHY_ID_SERDES)
- unsigned long regs;
- struct pci_dev *pdev;
- struct net_device *dev;
-#if TG3_VLAN_TAG_USED
- struct vlan_group *vlgrp;
-#endif
-
- struct tg3_rx_buffer_desc *rx_std;
- struct ring_info *rx_std_buffers;
- dma_addr_t rx_std_mapping;
-#if TG3_MINI_RING_WORKS
- struct tg3_rx_buffer_desc *rx_mini;
- struct ring_info *rx_mini_buffers;
- dma_addr_t rx_mini_mapping;
-#endif
- struct tg3_rx_buffer_desc *rx_jumbo;
- struct ring_info *rx_jumbo_buffers;
- dma_addr_t rx_jumbo_mapping;
-
- struct tg3_rx_buffer_desc *rx_rcb;
- dma_addr_t rx_rcb_mapping;
-
- /* TX descs are only used if TG3_FLAG_HOST_TXDS is set. */
- struct tg3_tx_buffer_desc *tx_ring;
- struct tx_ring_info *tx_buffers;
- dma_addr_t tx_desc_mapping;
-
- struct tg3_hw_status *hw_status;
- dma_addr_t status_mapping;
-
struct tg3_hw_stats *hw_stats;
dma_addr_t stats_mapping;
+
+ /* end "everything else" cacheline(s) section */
};
#endif /* !(_T3_H) */
===== include/linux/cache.h 1.5 vs edited =====
--- 1.5/include/linux/cache.h Tue Aug 27 16:04:10 2002
+++ edited/include/linux/cache.h Sat Dec 7 17:12:13 2002
@@ -53,4 +53,14 @@
#endif
#endif
+/* helper used inside struct definitions to break up struct at
+ * cacheline boundaries.
+ * Note: do not add a semi-colon (';') after an ALIGNED_PAD use.
+ */
+struct dummy_cacheline_struct {
+ int x;
+} ____cacheline_aligned;
+#define ALIGNED_PAD(name) \
+ struct dummy_cacheline_struct name;
+
#endif /* __LINUX_CACHE_H */
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