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Date:      Wed, 14 Aug 2013 20:20:42 +0000 (UTC)
From:      Navdeep Parhar <np@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-user@freebsd.org
Subject:   svn commit: r254336 - user/np/cxl_tuning/sys/netinet
Message-ID:  <201308142020.r7EKKgnT022557@svn.freebsd.org>
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Author: np
Date: Wed Aug 14 20:20:42 2013
New Revision: 254336
URL: http://svnweb.freebsd.org/changeset/base/254336

Log:
  Add a last-modified timestamp to each LRO entry and provide an interface
  to flush all inactive entries.  Drivers decide when to flush and what
  the inactivity threshold should be.
  
  Network drivers that process an rx queue to completion can enter a
  livelock type situation when the rate at which packets are received
  reaches equilibrium with the rate at which the rx thread is processing
  them.  When this happens the final LRO flush (normally when the rx
  routine is done) does not occur.  Pure ACKs and segments with total
  payload < 64K can get stuck in an LRO entry.  Symptoms are that TCP
  tx-mostly connections' performance falls off a cliff during heavy,
  unrelated rx on the interface.
  
  Flushing only inactive LRO entries works better than any of these
  alternates that I tried:
  - don't LRO pure ACKs
  - flush _all_ LRO entries periodically (every 'x' microseconds or every
    'y' descriptors)
  - stop rx processing in the driver periodically and schedule remaining
    work for later.

Modified:
  user/np/cxl_tuning/sys/netinet/tcp_lro.c
  user/np/cxl_tuning/sys/netinet/tcp_lro.h

Modified: user/np/cxl_tuning/sys/netinet/tcp_lro.c
==============================================================================
--- user/np/cxl_tuning/sys/netinet/tcp_lro.c	Wed Aug 14 19:34:13 2013	(r254335)
+++ user/np/cxl_tuning/sys/netinet/tcp_lro.c	Wed Aug 14 20:20:42 2013	(r254336)
@@ -194,6 +194,25 @@ tcp_lro_rx_csum_fixup(struct lro_entry *
 #endif
 
 void
+tcp_lro_flush_inactive(struct lro_ctrl *lc, const struct timeval *timeout)
+{
+	struct lro_entry *le, *le_tmp;
+	struct timeval tv;
+
+	if (SLIST_EMPTY(&lc->lro_active))
+		return;
+
+	getmicrotime(&tv);
+	timevalsub(&tv, timeout);
+	SLIST_FOREACH_SAFE(le, &lc->lro_active, next, le_tmp) {
+		if (timevalcmp(&tv, &le->mtime, >=)) {
+			SLIST_REMOVE(&lc->lro_active, le, lro_entry, next);
+			tcp_lro_flush(lc, le);
+		}
+	}
+}
+
+void
 tcp_lro_flush(struct lro_ctrl *lc, struct lro_entry *le)
 {
 
@@ -543,7 +562,8 @@ tcp_lro_rx(struct lro_ctrl *lc, struct m
 		if (le->p_len > (65535 - lc->ifp->if_mtu)) {
 			SLIST_REMOVE(&lc->lro_active, le, lro_entry, next);
 			tcp_lro_flush(lc, le);
-		}
+		} else
+			getmicrotime(&le->mtime);
 
 		return (0);
 	}
@@ -556,6 +576,7 @@ tcp_lro_rx(struct lro_ctrl *lc, struct m
 	le = SLIST_FIRST(&lc->lro_free);
 	SLIST_REMOVE_HEAD(&lc->lro_free, next);
 	SLIST_INSERT_HEAD(&lc->lro_active, le, next);
+	getmicrotime(&le->mtime);
 
 	/* Start filling in details. */
 	switch (eh_type) {

Modified: user/np/cxl_tuning/sys/netinet/tcp_lro.h
==============================================================================
--- user/np/cxl_tuning/sys/netinet/tcp_lro.h	Wed Aug 14 19:34:13 2013	(r254335)
+++ user/np/cxl_tuning/sys/netinet/tcp_lro.h	Wed Aug 14 20:20:42 2013	(r254336)
@@ -30,6 +30,8 @@
 #ifndef _TCP_LRO_H_
 #define _TCP_LRO_H_
 
+#include <sys/time.h>
+
 struct lro_entry
 {
 	SLIST_ENTRY(lro_entry)	next;
@@ -59,6 +61,7 @@ struct lro_entry
 	uint32_t		tsecr;
 	uint16_t		window;
 	uint16_t		timestamp;	/* flag, not a TCP hdr field. */
+	struct timeval		mtime;
 };
 SLIST_HEAD(lro_head, lro_entry);
 
@@ -83,6 +86,7 @@ struct lro_ctrl {
 
 int tcp_lro_init(struct lro_ctrl *);
 void tcp_lro_free(struct lro_ctrl *);
+void tcp_lro_flush_inactive(struct lro_ctrl *, const struct timeval *);
 void tcp_lro_flush(struct lro_ctrl *, struct lro_entry *);
 int tcp_lro_rx(struct lro_ctrl *, struct mbuf *, uint32_t);

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