From 950c54df1e503ece4e2987b0cf6e2e4e22817c0c Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Mon, 13 May 2013 12:01:22 +0000 Subject: 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 Reported-by: Heiko Carstens Signed-off-by: Ben Hutchings Acked-by: Geert Uytterhoeven Signed-off-by: David S. Miller --- drivers/net/ethernet/sfc/net_driver.h | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'drivers/net/ethernet/sfc/net_driver.h') diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h index 5efddf3c66e..39d6bd77f01 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; -- cgit v1.2.3-70-g09d2