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[net-next,41/44] Documentation: networking: Update ECN related sysctls

Message ID 20241015102940.26157-42-chia-yu.chang@nokia-bell-labs.com (mailing list archive)
State Changes Requested
Delegated to: Netdev Maintainers
Headers show
Series DualPI2, Accurate ECN, TCP Prague patch series | expand

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netdev/series_format fail Series longer than 15 patches
netdev/tree_selection success Clearly marked for net-next, async
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 5 this patch: 5
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers fail 5 maintainers not CCed: edumazet@google.com linux-doc@vger.kernel.org pabeni@redhat.com corbet@lwn.net kuba@kernel.org
netdev/build_clang success Errors and warnings before: 3 this patch: 3
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 3 this patch: 3
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 67 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Chia-Yu Chang (Nokia) Oct. 15, 2024, 10:29 a.m. UTC 
From: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>

Clarified that tcp_ecn enables ECN at IP and TCP layers, explained
IP and TCP layers differently, and fixed table (table headings don't
seem to render unless there's text in the first heading column).
Add tcp_ecn_option and tcp_ecn_option_beacon explantions.

Signed-off-by: Ilpo Järvinen <ij@kernel.org>
Co-developed-by: Bob Briscoe <research@bobbriscoe.net>
Signed-off-by: Bob Briscoe <research@bobbriscoe.net>
Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
---
 Documentation/networking/ip-sysctl.rst | 55 ++++++++++++++++++++------
 1 file changed, 44 insertions(+), 11 deletions(-)
diff mbox series

Patch

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index eacf8983e230..de6b57775140 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -422,23 +422,56 @@  tcp_early_retrans - INTEGER
 
 tcp_ecn - INTEGER
 	Control use of Explicit Congestion Notification (ECN) by TCP.
-	ECN is used only when both ends of the TCP connection indicate
-	support for it.  This feature is useful in avoiding losses due
-	to congestion by allowing supporting routers to signal
-	congestion before having to drop packets.
+	ECN is used only when both ends of the TCP connection indicate support
+	for it. This feature is useful in avoiding losses due to congestion by
+	allowing supporting routers to signal congestion before having to drop
+	packets. A host that supports ECN both sends ECN at the IP layer and
+	feeds back ECN at the TCP layer. The highest variant of ECN feedback
+	that both peers support is chosen by the ECN negotiation (Accurate ECN,
+	ECN, or no ECN).
+
+	The highest negotiated variant for incoming connection requests
+	and the highest variant requested by outgoing connection
+	attempts:
+
+	===== ==================== ====================
+	Value Incoming connections Outgoing connections
+	===== ==================== ====================
+	0     No ECN               No ECN
+	1     ECN                  ECN
+	2     ECN                  No ECN
+	3     AccECN               AccECN
+	4     AccECN               ECN
+	5     AccECN               No ECN
+	===== ==================== ====================
+
+	Default: 2
+
+tcp_ecn_option - INTEGER
+	Control Accurate ECN (AccECN) option sending when AccECN has been
+	successfully negotiated during handshake. Send logic inhibits
+	sending AccECN options regarless of this setting when no AccECN
+	option has been seen for the reverse direction.
 
 	Possible values are:
 
-		=  =====================================================
-		0  Disable ECN.  Neither initiate nor accept ECN.
-		1  Enable ECN when requested by incoming connections and
-		   also request ECN on outgoing connection attempts.
-		2  Enable ECN when requested by incoming connections
-		   but do not request ECN on outgoing connections.
-		=  =====================================================
+	= ============================================================
+	0 Never send AccECN option. This also disables sending AccECN
+	  option in SYN/ACK during handshake.
+	1 Send AccECN option sparingly according to the minimum option
+	  rules outlined in draft-ietf-tcpm-accurate-ecn.
+	2 Send AccECN option on every packet whenever it fits into TCP
+	  option space.
+	= ============================================================
 
 	Default: 2
 
+tcp_ecn_option_beacon - INTEGER
+	Control Accurate ECN (AccECN) option sending frequency per RTT and it
+	takes effect only when tcp_ecn_option is set to 2.
+
+	Default: 3 (AccECN will be send at least 3 times per RTT)
+
 tcp_ecn_fallback - BOOLEAN
 	If the kernel detects that ECN connection misbehaves, enable fall
 	back to non-ECN. Currently, this knob implements the fallback