netdev - [PATCH v2 net-next 5/5] xps: Documentation for transmit socketles flow steering

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Message-ID: <20160929035428.204355-6-tom@herbertland.com>
Date:   Wed, 28 Sep 2016 20:54:28 -0700
From:   Tom Herbert <tom@...bertland.com>
To:     <davem@...emloft.net>, <netdev@...r.kernel.org>
CC:     <kernel-team@...com>, <rick.jones2@....com>,
        <alexander.duyck@...il.com>
Subject: [PATCH v2 net-next 5/5] xps: Documentation for transmit socketles flow steering

Signed-off-by: Tom Herbert <tom@...bertland.com>
---
 Documentation/ABI/testing/sysfs-class-net |  8 ++++++++
 Documentation/networking/scaling.txt      | 26 ++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-net b/Documentation/ABI/testing/sysfs-class-net
index 668604f..0d2a6a9 100644
--- a/Documentation/ABI/testing/sysfs-class-net
+++ b/Documentation/ABI/testing/sysfs-class-net
@@ -251,3 +251,11 @@ Contact:	netdev@...r.kernel.org
 Description:
 		Indicates the unique physical switch identifier of a switch this
 		port belongs to, as a string.
+
+What:		/sys/class/net/<iface>/xps_dev_flow_table_cnt
+Date:		October 2016
+KernelVersion:	4.8
+Contact:	netdev@...r.kernel.org
+Description:
+		Indicates the number of entries in the XPS socketless flow
+		table.
diff --git a/Documentation/networking/scaling.txt b/Documentation/networking/scaling.txt
index 59f4db2..7f9590c 100644
--- a/Documentation/networking/scaling.txt
+++ b/Documentation/networking/scaling.txt
@@ -400,6 +400,26 @@ transport layer is responsible for setting ooo_okay appropriately. TCP,
 for instance, sets the flag when all data for a connection has been
 acknowledged.
 
+XPS: Transmit Socketless Flow Steering
+======================================
+
+Not all flows have an associated socket in which the transmit queue and
+ooo information can be saved. For instance, packets being transmitted over
+OVS for VMs do not have a socket that is visible to the kernel. To allow
+XPS to be effectively used a flow hash table is employed to save queue and
+ooo information for such socketless flows.
+
+The idea is that transmit queues are saved for socketless flows in a
+flow table that is indexed by skbuff hash. The flow table entries have
+two values: the queue_index and the head cnt of packets from the TX
+queue. When a packet is being sent without an associated socket the
+hash table is consulted which returns the queue_index to use. The
+returned queue is compared to the queue that would be selected by XPS.
+If they are are different the XPS queue is selected only if the tail cnt
+in the TX queue advances beyond the recorded head cnt. This checks if
+sending the packet on the new queue could cause ooo packets for the
+flow.
+
 ==== XPS Configuration
 
 XPS is only available if the kconfig symbol CONFIG_XPS is enabled (on by
@@ -409,6 +429,12 @@ queue is configured using the sysfs file entry:
 
 /sys/class/net/<dev>/queues/tx-<n>/xps_cpus
 
+Transmit socketless flow steering is enabled by setting the number of
+entries in the XPS flow table. This is configured in the sysfs file
+entry:
+
+/sys/class/net/<dev>/xps_dev_flow_table_cnt
+
 == Suggested Configuration
 
 For a network device with a single transmission queue, XPS configuration
-- 
2.9.3