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[iobuf] Relax alignment requirement for small I/O buffers
iPXE currently aligns all I/O buffers on a 2kB boundary. This is overkill for transmitted packets, which are typically much smaller than 2kB. Align I/O buffers on their own size. This reduces the alignment requirement for small buffers, while preserving the guarantee that I/O buffers will never cross boundaries that might cause problems for some DMA engines. Signed-off-by: Michael Brown <mcb30@ipxe.org>
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@ -19,6 +19,7 @@
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FILE_LICENCE ( GPL2_OR_LATER );
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#include <stdint.h>
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#include <strings.h>
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#include <errno.h>
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#include <ipxe/malloc.h>
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#include <ipxe/iobuf.h>
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@ -40,18 +41,24 @@ FILE_LICENCE ( GPL2_OR_LATER );
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*/
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struct io_buffer * alloc_iob ( size_t len ) {
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struct io_buffer *iobuf = NULL;
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size_t align;
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void *data;
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/* Pad to minimum length */
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if ( len < IOB_ZLEN )
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len = IOB_ZLEN;
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/* Align buffer length */
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len = ( len + __alignof__( *iobuf ) - 1 ) &
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~( __alignof__( *iobuf ) - 1 );
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/* Align buffer length to ensure that struct io_buffer is aligned */
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len = ( len + __alignof__ ( *iobuf ) - 1 ) &
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~( __alignof__ ( *iobuf ) - 1 );
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/* Align buffer on its own size to avoid potential problems
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* with boundary-crossing DMA.
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*/
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align = ( 1 << fls ( len - 1 ) );
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/* Allocate memory for buffer plus descriptor */
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data = malloc_dma ( len + sizeof ( *iobuf ), IOB_ALIGN );
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data = malloc_dma ( len + sizeof ( *iobuf ), align );
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if ( ! data )
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return NULL;
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@ -61,6 +68,7 @@ struct io_buffer * alloc_iob ( size_t len ) {
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return iobuf;
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}
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/**
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* Free I/O buffer
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*
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@ -13,17 +13,6 @@ FILE_LICENCE ( GPL2_OR_LATER );
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#include <assert.h>
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#include <ipxe/list.h>
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/**
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* I/O buffer alignment
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*
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* I/O buffers allocated via alloc_iob() are guaranteed to be
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* physically aligned to this boundary. Some cards cannot DMA across
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* a 4kB boundary. With a standard Ethernet MTU, aligning to a 2kB
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* boundary is sufficient to guarantee no 4kB boundary crossings. For
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* a jumbo Ethernet MTU, a packet may be larger than 4kB anyway.
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*/
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#define IOB_ALIGN 2048
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/**
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* Minimum I/O buffer length
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*
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