netdev - [PATCH] Documentation: clarify tcp

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Message-ID: <20080710200510.GE27734@fieldses.org>
Date:	Thu, 10 Jul 2008 16:05:10 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Jonathan Corbet <corbet@....net>
Cc:	Bill Fink <billfink@...dspring.com>,
	Stephen Hemminger <stephen.hemminger@...tta.com>,
	Roland Dreier <rdreier@...co.com>,
	David Miller <davem@...emloft.net>, aglo@...i.umich.edu,
	shemminger@...tta.com, netdev@...r.kernel.org, rees@...ch.edu,
	Evgeniy Polyakov <johnpol@....mipt.ru>
Subject: [PATCH] Documentation: clarify tcp_{r,w}mem sysctl docs

From: J. Bruce Fields <bfields@...i.umich.edu>
Date: Wed, 9 Jul 2008 18:28:48 -0400

Fix some of the defaults and attempt to clarify some language.

Signed-off-by: J. Bruce Fields <bfields@...i.umich.edu>
Cc: Evgeniy Polyakov <johnpol@....mipt.ru>
---
 Documentation/networking/ip-sysctl.txt |   26 +++++++++++++++-----------
 1 files changed, 15 insertions(+), 11 deletions(-)

On Thu, Jul 10, 2008 at 05:06:50AM +0400, Evgeniy Polyakov wrote:
> On Wed, Jul 09, 2008 at 06:28:02PM -0400, J. Bruce Fields
> (bfields@...ldses.org) wrote:
> > OK, thanks.  Would the following be any more clearer and/or
> > accurate?
>
> Looks good, thank you :)
> It is likely the first ever mention of the fact, that SO_RECV/SNDBUF
> disables autotuning.

OK!  Uh, I'm assuming Jon Corbet's documentation tree would be a
reasonable route to submit this by....

--b.

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 17a6e46..a22af04 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -336,7 +336,7 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max
 	pressure.
 	Default: 8K
 
-	default: default size of receive buffer used by TCP sockets.
+	default: initial size of receive buffer used by TCP sockets.
 	This value overrides net.core.rmem_default used by other protocols.
 	Default: 87380 bytes. This value results in window of 65535 with
 	default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
@@ -344,8 +344,10 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max
 
 	max: maximal size of receive buffer allowed for automatically
 	selected receiver buffers for TCP socket. This value does not override
-	net.core.rmem_max, "static" selection via SO_RCVBUF does not use this.
-	Default: 87380*2 bytes.
+	net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
+	automatic tuning of that socket's receive buffer size, in which
+	case this value is ignored.
+	Default: between 87380B and 4MB, depending on RAM size.
 
 tcp_sack - BOOLEAN
 	Enable select acknowledgments (SACKS).
@@ -419,19 +421,21 @@ tcp_window_scaling - BOOLEAN
 	Enable window scaling as defined in RFC1323.
 
 tcp_wmem - vector of 3 INTEGERs: min, default, max
-	min: Amount of memory reserved for send buffers for TCP socket.
+	min: Amount of memory reserved for send buffers for TCP sockets.
 	Each TCP socket has rights to use it due to fact of its birth.
 	Default: 4K
 
-	default: Amount of memory allowed for send buffers for TCP socket
-	by default. This value overrides net.core.wmem_default used
-	by other protocols, it is usually lower than net.core.wmem_default.
+	default: initial size of send buffer used by TCP sockets.  This
+	value overrides net.core.wmem_default used by other protocols.
+	It is usually lower than net.core.wmem_default.
 	Default: 16K
 
-	max: Maximal amount of memory allowed for automatically selected
-	send buffers for TCP socket. This value does not override
-	net.core.wmem_max, "static" selection via SO_SNDBUF does not use this.
-	Default: 128K
+	max: Maximal amount of memory allowed for automatically tuned
+	send buffers for TCP sockets. This value does not override
+	net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
+	automatic tuning of that socket's send buffer size, in which case
+	this value is ignored.
+	Default: between 64K and 4MB, depending on RAM size.
 
 tcp_workaround_signed_windows - BOOLEAN
 	If set, assume no receipt of a window scaling option means the
-- 
1.5.5.rc1

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