[iobuf] Allocate I/O buffer descriptor separately to conserve aligned memory
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>
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@ -40,7 +40,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
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* @c IOBUF_SIZE.
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* @c IOBUF_SIZE.
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*/
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*/
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struct io_buffer * alloc_iob ( size_t len ) {
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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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struct io_buffer *iobuf;
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size_t align;
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size_t align;
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void *data;
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void *data;
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@ -57,14 +57,37 @@ struct io_buffer * alloc_iob ( size_t len ) {
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*/
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*/
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align = ( 1 << fls ( len - 1 ) );
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align = ( 1 << fls ( len - 1 ) );
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/* Allocate memory for buffer plus descriptor */
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/* Allocate buffer plus descriptor as a single unit, unless
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data = malloc_dma ( len + sizeof ( *iobuf ), align );
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* doing so will push the total size over the alignment
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if ( ! data )
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* boundary.
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return NULL;
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*/
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if ( ( len + sizeof ( *iobuf ) ) <= align ) {
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iobuf = ( struct io_buffer * ) ( data + len );
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/* Allocate memory for buffer plus descriptor */
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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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iobuf = ( data + len );
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} else {
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/* Allocate memory for buffer */
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data = malloc_dma ( len, align );
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if ( ! data )
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return NULL;
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/* Allocate memory for descriptor */
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iobuf = malloc ( sizeof ( *iobuf ) );
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if ( ! iobuf ) {
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free_dma ( data, len );
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return NULL;
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}
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}
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/* Populate descriptor */
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iobuf->head = iobuf->data = iobuf->tail = data;
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iobuf->head = iobuf->data = iobuf->tail = data;
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iobuf->end = iobuf;
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iobuf->end = ( data + len );
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return iobuf;
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return iobuf;
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}
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}
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@ -75,12 +98,29 @@ struct io_buffer * alloc_iob ( size_t len ) {
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* @v iobuf I/O buffer
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* @v iobuf I/O buffer
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*/
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*/
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void free_iob ( struct io_buffer *iobuf ) {
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void free_iob ( struct io_buffer *iobuf ) {
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if ( iobuf ) {
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size_t len;
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assert ( iobuf->head <= iobuf->data );
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assert ( iobuf->data <= iobuf->tail );
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/* Allow free_iob(NULL) to be valid */
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assert ( iobuf->tail <= iobuf->end );
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if ( ! iobuf )
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free_dma ( iobuf->head,
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return;
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( iobuf->end - iobuf->head ) + sizeof ( *iobuf ) );
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/* Sanity checks */
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assert ( iobuf->head <= iobuf->data );
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assert ( iobuf->data <= iobuf->tail );
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assert ( iobuf->tail <= iobuf->end );
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/* Free buffer */
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len = ( iobuf->end - iobuf->head );
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if ( iobuf->end == iobuf ) {
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/* Descriptor is inline */
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free_dma ( iobuf->head, ( len + sizeof ( *iobuf ) ) );
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} else {
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/* Descriptor is detached */
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free_dma ( iobuf->head, len );
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free ( iobuf );
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}
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}
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}
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}
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