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authorBen Hutchings <bhutchings@solarflare.com>2013-05-13 12:01:22 +0000
committerDavid S. Miller <davem@davemloft.net>2013-05-14 11:32:04 -0700
commit950c54df1e503ece4e2987b0cf6e2e4e22817c0c (patch)
tree5349a53cb2266a51dc67107e3182938e1f338ba6 /drivers/net/ethernet/sfc
parentc14ff2ea2d5818c811e5c6e67e794df4a71a6094 (diff)
sfc: Reduce RX scatter buffer size, and reduce alignment if appropriate
efx_start_datapath() asserts that we can fit 2 RX scatter buffers plus a software structure, each appropriately aligned, into a single page. Where L1_CACHE_BYTES == 256 and PAGE_SIZE == 4096, which is the case on s390, this assertion fails. The current scatter buffer size is also not a multiple of 64 or 128, which are more common cache line sizes. If we can make both the start and end of a scatter buffer cache-aligned, this will reduce the need for read-modify-write operations on inter- processor links. Fix the alignment by reducing EFX_RX_USR_BUF_SIZE to 2048 - 256 == 1792. (We could use 2048 - L1_CACHE_BYTES, but EFX_RX_USR_BUF_SIZE also affects user-level networking where a larger amount of housekeeping data may be needed. Although this version of the driver does not support user-level networking, I prefer to keep scattering behaviour consistent with the out-of-tree version.) This still doesn't fix the s390 build because like most architectures it has NET_IP_ALIGN == 2. When NET_IP_ALIGN != 0 we cannot achieve cache line alignment at either the start or end of a scatter buffer, so there is actually no point in padding the buffers to a multiple of the cache line size. All we need is 4-byte alignment of the network header, so do that. Adjust the assertions accordingly. Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Ben Hutchings <bhutchings@solarflare.com> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net/ethernet/sfc')
-rw-r--r--drivers/net/ethernet/sfc/efx.c6
-rw-r--r--drivers/net/ethernet/sfc/net_driver.h16
-rw-r--r--drivers/net/ethernet/sfc/rx.c2
3 files changed, 19 insertions, 5 deletions
diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index 999289bb2eb9..39e4cb39de29 100644
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -643,9 +643,11 @@ static void efx_start_datapath(struct efx_nic *efx)
efx->rx_scatter = false;
efx->rx_buffer_order = 0;
} else if (efx->type->can_rx_scatter) {
+ BUILD_BUG_ON(EFX_RX_USR_BUF_SIZE % L1_CACHE_BYTES);
BUILD_BUG_ON(sizeof(struct efx_rx_page_state) +
- NET_IP_ALIGN + EFX_RX_USR_BUF_SIZE >
- PAGE_SIZE / 2);
+ 2 * ALIGN(NET_IP_ALIGN + EFX_RX_USR_BUF_SIZE,
+ EFX_RX_BUF_ALIGNMENT) >
+ PAGE_SIZE);
efx->rx_scatter = true;
efx->rx_dma_len = EFX_RX_USR_BUF_SIZE;
efx->rx_buffer_order = 0;
diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index 5efddf3c66e9..39d6bd77f015 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -72,8 +72,20 @@
/* Maximum possible MTU the driver supports */
#define EFX_MAX_MTU (9 * 1024)
-/* Size of an RX scatter buffer. Small enough to pack 2 into a 4K page. */
-#define EFX_RX_USR_BUF_SIZE 1824
+/* Size of an RX scatter buffer. Small enough to pack 2 into a 4K page,
+ * and should be a multiple of the cache line size.
+ */
+#define EFX_RX_USR_BUF_SIZE (2048 - 256)
+
+/* If possible, we should ensure cache line alignment at start and end
+ * of every buffer. Otherwise, we just need to ensure 4-byte
+ * alignment of the network header.
+ */
+#if NET_IP_ALIGN == 0
+#define EFX_RX_BUF_ALIGNMENT L1_CACHE_BYTES
+#else
+#define EFX_RX_BUF_ALIGNMENT 4
+#endif
/* Forward declare Precision Time Protocol (PTP) support structure. */
struct efx_ptp_data;
diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 99f70dd55fc8..a7dfe36cabf4 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -94,7 +94,7 @@ static inline void efx_sync_rx_buffer(struct efx_nic *efx,
void efx_rx_config_page_split(struct efx_nic *efx)
{
efx->rx_page_buf_step = ALIGN(efx->rx_dma_len + NET_IP_ALIGN,
- L1_CACHE_BYTES);
+ EFX_RX_BUF_ALIGNMENT);
efx->rx_bufs_per_page = efx->rx_buffer_order ? 1 :
((PAGE_SIZE - sizeof(struct efx_rx_page_state)) /
efx->rx_page_buf_step);