Author: glebius
Date: Mon Jun 4 12:49:21 2012
New Revision: 236560
URL: http://svn.freebsd.org/changeset/base/236560
Log:
Optimise kern_sendfile(): skip cycling through the entire mbuf chain in
m_cat(), storing pointer to last mbuf in chain in local variable and
attaching new mbuf to the end of chain.
Submitter reports that CPU load dropped for > 10% on a web server
serving large files with this optimisation.
Submitted by: Sergey Budnevitch <sb nginx.com>
Modified:
head/sys/kern/uipc_syscalls.c
Modified: head/sys/kern/uipc_syscalls.c
==============================================================================
--- head/sys/kern/uipc_syscalls.c Mon Jun 4 12:36:58 2012
(r236559)
+++ head/sys/kern/uipc_syscalls.c Mon Jun 4 12:49:21 2012
(r236560)
@@ -1962,6 +1962,7 @@ kern_sendfile(struct thread *td, struct
* and takes care of the overall progress.
*/
for (off = uap->offset, rem = uap->nbytes; ; ) {
+ struct mbuf *mtail = NULL;
int loopbytes = 0;
int space = 0;
int done = 0;
@@ -2181,10 +2182,15 @@ retry_space:
m0->m_len = xfsize;
/* Append to mbuf chain. */
- if (m != NULL)
- m_cat(m, m0);
- else
- m = m0;
+ if (mtail != NULL) {
+ mtail->m_next = m0;
+ } else {
+ if (m != NULL)
+ m_cat(m, m0);
+ else
+ m = m0;
+ }
+ mtail = m0;
/* Keep track of bits processed. */
loopbytes += xfsize;
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