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[iobuf] Relax alignment requirement for small I/O buffers

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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>
This commit is contained in:
Michael Brown
2012-06-29 16:07:12 +01:00
parent 9a8c6b00d4
commit a5c016d93e
2 changed files with 13 additions and 16 deletions
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11
src/include/ipxe/iobuf.h
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@@ -13,17 +13,6 @@ FILE_LICENCE ( GPL2_OR_LATER );
#include <assert.h>
#include <ipxe/list.h>
/**
* I/O buffer alignment
*
* I/O buffers allocated via alloc_iob() are guaranteed to be
* physically aligned to this boundary. Some cards cannot DMA across
* a 4kB boundary. With a standard Ethernet MTU, aligning to a 2kB
* boundary is sufficient to guarantee no 4kB boundary crossings. For
* a jumbo Ethernet MTU, a packet may be larger than 4kB anyway.
*/
#define IOB_ALIGN 2048
/**
* Minimum I/O buffer length
*