Re: Socket buffer sizes with autotuning

["John Heffner" <johnwheffner@gmail.com>]

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On Mon, Apr 28, 2008 at 11:30 AM, Jerry Chu <hkchu@google.com> wrote:
>  Correct, but its counterpart doesn't exist in tcp_is_cwnd_limited(). So
>  cwnd will continue to grow when left < cwnd/sysctl_tcp_tso_win_divisor,
>  which can be very large when cwnd is large.
>
>  If I change tcp_tso_win_divisor to 0, cwnd max out at 695 rather than 1037,
>  exactly off by 1/3. I tried to add the same check to tcp_is_cwnd_limited():
>
>  diff -c /tmp/tcp.h.old tcp.h
>  *** /tmp/tcp.h.old      Mon Apr 28 11:00:44 2008
>  --- tcp.h       Mon Apr 28 10:54:10 2008
>  ***************
>  *** 828,833 ****
>  --- 828,835 ----
>                 return 0;
>
>         left = tp->snd_cwnd - in_flight;
>  +       if (left >= 65536)
>  +               return 0;
>         if (sysctl_tcp_tso_win_divisor)
>                 return left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd;
>         else
>
>  >
>
>  But it doesn't seem to help (cwnd still grows to 1037).

Cwnd is in packets, not bytes.

Try this series of patches, against net-next.

  -John

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From 57039cfc486ae4deac3b1fecaa238b5483c034df Mon Sep 17 00:00:00 2001
From: John Heffner <johnwheffner@gmail.com>
Date: Mon, 28 Apr 2008 12:17:49 -0700
Subject: [PATCH 1/2] [NET]: Allow send-limited cwnd to grow up to max_burst when gso disabled

This changes the logic in tcp_is_cwnd_limited() so that cwnd may grow
up to tcp_max_burst() even when sk_can_gso() is false, or when
sysctl_tcp_tso_win_divisor != 0.

Signed-off-by: John Heffner <johnwheffner@gmail.com>
---
 net/ipv4/tcp_cong.c |   11 ++++-------
 1 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 3a6be23..bfb1996 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -285,14 +285,11 @@ int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
 	if (in_flight >= tp->snd_cwnd)
 		return 1;
 
-	if (!sk_can_gso(sk))
-		return 0;
-
 	left = tp->snd_cwnd - in_flight;
-	if (sysctl_tcp_tso_win_divisor)
-		return left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd;
-	else
-		return left <= tcp_max_burst(tp);
+	if (sk_can_gso(sk) &&
+	    left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd)
+		return 1;
+	return left <= tcp_max_burst(tp);
 }
 EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
 
-- 
1.5.2.5


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From fc1d9fe99748f3811a0a5b9d93463cf0e4788f56 Mon Sep 17 00:00:00 2001
From: John Heffner <johnwheffner@gmail.com>
Date: Mon, 28 Apr 2008 12:19:22 -0700
Subject: [PATCH 2/2] [NET]: Limit cwnd growth when deferring for GSO

This fixes inappropriately large cwnd growth on sender-limited flows
when GSO is enabled, limiting cwnd growth to 64k.

Signed-off-by: John Heffner <johnwheffner@gmail.com>
---
 net/ipv4/tcp_cong.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index bfb1996..6a25082 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -287,7 +287,8 @@ int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
 
 	left = tp->snd_cwnd - in_flight;
 	if (sk_can_gso(sk) &&
-	    left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd)
+	    left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
+	    left * tp->mss_cache < sk->sk_gso_max_size)
 		return 1;
 	return left <= tcp_max_burst(tp);
 }
-- 
1.5.2.5