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[iobuf] Allocate I/O buffer descriptor separately to conserve aligned memory

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I/O buffers are allocated on aligned boundaries.  The I/O buffer
descriptor (the struct io_buffer) is currently attached to the end of
the I/O buffer.  When the size of the buffer is close to its
alignment, this can waste large amounts of aligned memory.

For example, a network card using 2048-byte receive buffers will end
up allocating 2072 bytes on a 2048-byte boundary.  This effectively
wastes 50% of the available memory.

Improve the situation by allocating the descriptor separately from the
main I/O buffer if inline allocation would cause the total allocated
size to cross the alignment boundary.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown 2012-07-08 17:14:08 +01:00
parent b0e236a9ee
commit 4a8a7bd91a
1 changed files with 53 additions and 13 deletions
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52
src/core/iobuf.c
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@ -40,7 +40,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
* @c IOBUF_SIZE.
*/
struct io_buffer * alloc_iob ( size_t len ) {
struct io_buffer *iobuf = NULL;
struct io_buffer *iobuf;
size_t align;
void *data;
@ -57,14 +57,37 @@ struct io_buffer * alloc_iob ( size_t len ) {
*/
align = ( 1 << fls ( len - 1 ) );
/* Allocate buffer plus descriptor as a single unit, unless
* doing so will push the total size over the alignment
* boundary.
*/
if ( ( len + sizeof ( *iobuf ) ) <= align ) {
/* Allocate memory for buffer plus descriptor */
data = malloc_dma ( len + sizeof ( *iobuf ), align );
if ( ! data )
return NULL;
iobuf = ( data + len );
iobuf = ( struct io_buffer * ) ( data + len );
} else {
/* Allocate memory for buffer */
data = malloc_dma ( len, align );
if ( ! data )
return NULL;
/* Allocate memory for descriptor */
iobuf = malloc ( sizeof ( *iobuf ) );
if ( ! iobuf ) {
free_dma ( data, len );
return NULL;
}
}
/* Populate descriptor */
iobuf->head = iobuf->data = iobuf->tail = data;
iobuf->end = iobuf;
iobuf->end = ( data + len );
return iobuf;
}
@ -75,12 +98,29 @@ struct io_buffer * alloc_iob ( size_t len ) {
* @v iobuf I/O buffer
*/
void free_iob ( struct io_buffer *iobuf ) {
if ( iobuf ) {
size_t len;
/* Allow free_iob(NULL) to be valid */
if ( ! iobuf )
return;
/* Sanity checks */
assert ( iobuf->head <= iobuf->data );
assert ( iobuf->data <= iobuf->tail );
assert ( iobuf->tail <= iobuf->end );
free_dma ( iobuf->head,
( iobuf->end - iobuf->head ) + sizeof ( *iobuf ) );
/* Free buffer */
len = ( iobuf->end - iobuf->head );
if ( iobuf->end == iobuf ) {
/* Descriptor is inline */
free_dma ( iobuf->head, ( len + sizeof ( *iobuf ) ) );
} else {
/* Descriptor is detached */
free_dma ( iobuf->head, len );
free ( iobuf );
}
}