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[slam] Speed up NACK transmission by restricting the block-list length 

Shorter NACK packets take less time to construct and spew out less
debug output, and there's a limit to how useful it is to send a
complete missing-block list anyway; if the loss rate is high then
we're going to have to retransmit an updated missing-block list
anyway.

Also add pretty debugging output to show the list of requested blocks.
This commit is contained in:
Michael Brown 2008-06-10 11:23:34 +01:00
parent 81d92d5181
commit 1e5c2d48cb
1 changed files with 63 additions and 21 deletions
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84
src/net/udp/slam.c
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@ -93,6 +93,16 @@ FEATURE ( FEATURE_PROTOCOL, "SLAM", DHCP_EB_FEATURE_SLAM, 1 );
#define SLAM_MAX_HEADER_LEN ( 8 /* transaction id */ + 8 /* total_bytes */ + \
8 /* block_size */ )
/** Maximum SLAM NACK length
*
* This is a policy decision. Shorter packets take less time to
* construct and spew out less debug output, and there's a limit to
* how useful it is to send a complete missing-block list anyway; if
* the loss rate is high then we're going to have to retransmit an
* updated missing-block list anyway.
*/
#define SLAM_MAX_NACK_LEN 16
/** A SLAM request */
struct slam_request {
/** Reference counter */
@ -198,8 +208,8 @@ static int slam_put_value ( struct slam_request *slam,
*/
len = ( ( flsl ( value ) + 10 ) / 8 );
if ( len >= iob_tailroom ( iobuf ) ) {
DBGC ( slam, "SLAM %p cannot add %d-byte value\n",
slam, len );
DBGC2 ( slam, "SLAM %p cannot add %d-byte value\n",
slam, len );
return -ENOBUFS;
}
/* There is no valid way within the protocol that we can end
@ -220,6 +230,52 @@ static int slam_put_value ( struct slam_request *slam,
return 0;
}
/**
* Build SLAM compressed missing-block list
*
* @v slam SLAM request
* @v iobuf I/O buffer
* @ret rc Return status code
*/
static int slam_build_block_list ( struct slam_request *slam,
struct io_buffer *iobuf ) {
unsigned int block;
unsigned int block_count;
int block_present;
int last_block_present;
int rc;
DBGC ( slam, "SLAM %p asking for ", slam );
/* Walk bitmap to construct list */
block_count = 0;
last_block_present = ( ! 0 );
for ( block = 0 ; block < slam->num_blocks ; block++ ) {
block_present = ( !! bitmap_test ( &slam->bitmap, block ) );
if ( block_present != last_block_present ) {
if ( ( rc = slam_put_value ( slam, iobuf,
block_count ) ) != 0 ) {
DBGC ( slam, "...\n" );
return rc;
}
DBGC ( slam, "%c%d",
( last_block_present ? ' ' : '-' ),
( last_block_present ? block : block - 1 ) );
block_count = 0;
last_block_present = block_present;
}
block_count++;
}
if ( ( rc = slam_put_value ( slam, iobuf, block_count ) ) != 0 ) {
DBGC ( slam, "...\n" );
return rc;
}
DBGC ( slam, "%c%d\n", ( last_block_present ? ' ' : '-' ),
( last_block_present ? block : block - 1 ) );
return 0;
}
/**
* Send SLAM NACK packet
*
@ -228,10 +284,6 @@ static int slam_put_value ( struct slam_request *slam,
*/
static int slam_tx_nack ( struct slam_request *slam ) {
struct io_buffer *iobuf;
unsigned int block;
unsigned int block_count;
int block_present;
int last_block_present;
uint8_t *nul;
DBGC ( slam, "SLAM %p transmitting NACK\n", slam );
@ -243,26 +295,17 @@ static int slam_tx_nack ( struct slam_request *slam ) {
* data we can fit in a packet. If we overrun, it seems to be
* acceptable to drop information anyway.
*/
iobuf = xfer_alloc_iob ( &slam->socket, slam->block_size );
iobuf = xfer_alloc_iob ( &slam->socket, SLAM_MAX_NACK_LEN );
if ( ! iobuf ) {
DBGC ( slam, "SLAM %p could not allocate I/O buffer\n",
slam );
return -ENOMEM;
}
/* Walk bitmap to construct list */
block_count = 0;
last_block_present = ( ! 0 );
for ( block = 0 ; block < slam->num_blocks ; block++ ) {
block_present = ( !! bitmap_test ( &slam->bitmap, block ) );
if ( block_present != last_block_present ) {
slam_put_value ( slam, iobuf, block_count );
block_count = 0;
last_block_present = block_present;
}
block_count++;
}
slam_put_value ( slam, iobuf, block_count );
/* Build block list. (Errors are non-fatal; it just means we
* couldn't fit the compressed list within the packet.)
*/
slam_build_block_list ( slam, iobuf );
/* Add NUL terminator */
nul = iob_put ( iobuf, 1 );
@ -697,7 +740,6 @@ static int slam_open ( struct xfer_interface *xfer, struct uri *uri ) {
/* Fake an invalid cached header of { 0x00, ... } */
slam->header_len = 1;
/* Fake parameters for initial NACK */
slam->block_size = 512;
slam->num_blocks = 1;
if ( ( rc = bitmap_resize ( &slam->bitmap, 1 ) ) != 0 ) {
DBGC ( slam, "SLAM %p could not allocate initial bitmap: "