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Add CA message header size optimisation.

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If a packet is sufficiently small it can be worth the small
optimisation of saving the 8 bytes in a large packet header.
This commit is contained in:
Michael Abbott
2010-08-11 17:37:30 -05:00
committed by Andrew Johnson
parent b2374f583b 9d9ba1a442
commit 0291900562
1 changed files with 17 additions and 2 deletions
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19
src/rsrv/caserverio.c
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@@ -33,6 +33,10 @@
#define epicsExportSharedSymbols
#include "server.h"
/* As an optimisation, any message allocated with a large header is resized to
* use a small header if the payload size is below this threshold. */
#define SMALL_MESSAGE_THRESHOLD 65
/*
* cas_send_bs_msg()
*
@@ -350,8 +354,19 @@ void cas_commit_msg ( struct client *pClient, ca_uint32_t size )
if ( pMsg->m_postsize == htons ( 0xffff ) ) {
ca_uint32_t * pLW = ( ca_uint32_t * ) ( pMsg + 1 );
assert ( size <= ntohl ( *pLW ) );
pLW[0] = htonl ( size );
size += sizeof ( caHdr ) + 2 * sizeof ( *pLW );
if (size < SMALL_MESSAGE_THRESHOLD) {
/* If the message is sufficiently small it can be worth converting a
* large message header into a small header. This saves us all of 8
* bytes over the wire, so it's not such a big deal. */
pMsg->m_postsize = htons((ca_uint16_t) size);
pMsg->m_count = htons((ca_uint16_t) ntohl(pLW[1]));
memmove(pLW, pLW + 2, size);
size += sizeof(caHdr);
}
else {
pLW[0] = htonl ( size );
size += sizeof ( caHdr ) + 2 * sizeof ( *pLW );
}
}
else {
assert ( size <= ntohs ( pMsg->m_postsize ) );