From: Stefan Richter Date: Sun, 4 Feb 2007 12:04:32 +0000 (+0100) Subject: ieee1394: sbp2: remove unnecessary alignments of struct members X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=f412bf440be2dfc0f0ded917410c599c002549e0;p=linux-beck.git ieee1394: sbp2: remove unnecessary alignments of struct members The members "dma_addr_t command_orb_dma" and "dma_addr_t sge_dma" of sbp2.h::sbp2_command_info do not have to be aligned themselves --- only the memory which they point to has to be. The member "struct sbp2_command_orb command_orb" has to be aligned on 4 bytes boundary which is guaranteed because it contains u32 members. The member "struct sbp2_unrestricted_page_table scatter_gather_element", i.e. the SBP-2 s/g table, has to be aligned on 8 bytes boundary according to the SBP-2 spec. This is not a requirement for FireWire controllers but could be expected by SBP-2 targets. I see no need to align the members command_orb and scatter_gather_element on CPU cacheline boundaries. It could have performance benefits, but on the other hand sbp2 has a somewhat wasteful allocation scheme which should be optimized first before further tweaks like cacheline alignments. (E.g. don't always allocate SG_ALL s/g table elements.) Note, before as well as after the patch, the code relies on the assumption that memory alignment in the virtual address space is preserved in the physical address space after DMA mapping. Signed-off-by: Stefan Richter --- diff --git a/drivers/ieee1394/sbp2.h b/drivers/ieee1394/sbp2.h index 9ae842329bf3..44402b9d82a8 100644 --- a/drivers/ieee1394/sbp2.h +++ b/drivers/ieee1394/sbp2.h @@ -250,15 +250,15 @@ enum sbp2_dma_types { /* Per SCSI command */ struct sbp2_command_info { struct list_head list; - struct sbp2_command_orb command_orb ____cacheline_aligned; - dma_addr_t command_orb_dma ____cacheline_aligned; + struct sbp2_command_orb command_orb; + dma_addr_t command_orb_dma; struct scsi_cmnd *Current_SCpnt; void (*Current_done)(struct scsi_cmnd *); /* Also need s/g structure for each sbp2 command */ struct sbp2_unrestricted_page_table - scatter_gather_element[SG_ALL] ____cacheline_aligned; - dma_addr_t sge_dma ____cacheline_aligned; + scatter_gather_element[SG_ALL] __attribute__((aligned(8))); + dma_addr_t sge_dma; void *sge_buffer; dma_addr_t cmd_dma; enum sbp2_dma_types dma_type;