4a8a7bd91a
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>
145 lines
3.3 KiB
C
145 lines
3.3 KiB
C
/*
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* Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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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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/** @file
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*
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* I/O buffers
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*
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*/
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/**
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* Allocate I/O buffer
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*
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* @v len Required length of buffer
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* @ret iobuf I/O buffer, or NULL if none available
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*
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* The I/O buffer will be physically aligned to a multiple of
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* @c IOBUF_SIZE.
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*/
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struct io_buffer * alloc_iob ( size_t len ) {
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struct io_buffer *iobuf;
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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 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 buffer plus descriptor as a single unit, unless
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* doing so will push the total size over the alignment
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* boundary.
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*/
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if ( ( len + sizeof ( *iobuf ) ) <= align ) {
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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->end = ( data + 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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* @v iobuf I/O buffer
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*/
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void free_iob ( struct io_buffer *iobuf ) {
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size_t len;
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/* Allow free_iob(NULL) to be valid */
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if ( ! iobuf )
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return;
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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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* Ensure I/O buffer has sufficient headroom
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*
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* @v iobuf I/O buffer
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* @v len Required headroom
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*
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* This function currently only checks for the required headroom; it
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* does not reallocate the I/O buffer if required. If we ever have a
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* code path that requires this functionality, it's a fairly trivial
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* change to make.
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*/
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int iob_ensure_headroom ( struct io_buffer *iobuf, size_t len ) {
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if ( iob_headroom ( iobuf ) >= len )
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return 0;
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return -ENOBUFS;
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}
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