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From: Gleb Smirnoff <glebius@FreeBSD.org>
Date: Thu, 14 Jun 2012 07:51:37 +0000 (UTC)
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Subject: svn commit: r237054 - stable/9/sys/kern
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Author: glebius
Date: Thu Jun 14 07:51:37 2012
New Revision: 237054
URL: http://svn.freebsd.org/changeset/base/237054

Log:
  Merge 236560 and following 236563,236598 from head:
    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:
  stable/9/sys/kern/uipc_syscalls.c
Directory Properties:
  stable/9/sys/   (props changed)

Modified: stable/9/sys/kern/uipc_syscalls.c
==============================================================================
--- stable/9/sys/kern/uipc_syscalls.c	Thu Jun 14 07:40:18 2012	(r237053)
+++ stable/9/sys/kern/uipc_syscalls.c	Thu Jun 14 07:51:37 2012	(r237054)
@@ -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 +2182,13 @@ retry_space:
 			m0->m_len = xfsize;
 
 			/* Append to mbuf chain. */
-			if (m != NULL)
-				m_cat(m, m0);
+			if (mtail != NULL)
+				mtail->m_next = m0;
+			else if (m != NULL)
+				m_last(m)->m_next = m0;
 			else
 				m = m0;
+			mtail = m0;
 
 			/* Keep track of bits processed. */
 			loopbytes += xfsize;