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    Subject[RFC V2 PATCH 25/25] Documentation/networking: Document NET policy
    Date
    From: Kan Liang <kan.liang@intel.com>

    Signed-off-by: Kan Liang <kan.liang@intel.com>
    ---
    Documentation/networking/netpolicy.txt | 157 +++++++++++++++++++++++++++++++++
    1 file changed, 157 insertions(+)
    create mode 100644 Documentation/networking/netpolicy.txt

    diff --git a/Documentation/networking/netpolicy.txt b/Documentation/networking/netpolicy.txt
    new file mode 100644
    index 0000000..b8e3d4c
    --- /dev/null
    +++ b/Documentation/networking/netpolicy.txt
    @@ -0,0 +1,157 @@
    +What is Linux Net Policy?
    +
    +It is a big challenge to get good network performance. First, the network
    +performance is not good with default system settings. Second, it is too
    +difficult to do automatic tuning for all possible workloads, since workloads
    +have different requirements. Some workloads may want high throughput. Some may
    +need low latency. Last but not least, there are lots of manual configurations.
    +Fine grained configuration is too difficult for users.
    +
    +"NET policy" intends to simplify the network configuration and get a
    +good network performance according to the hints(policy) which is applied by
    +user. It provides some typical "policies" for user which can be set
    +per-socket, per-task or per-device. The kernel automatically figures out
    +how to merge different requests to get good network performance.
    +
    +"Net policy" is designed for multiqueue network devices. This document
    +describes the concepts and APIs of "net policy" support.
    +
    +NET POLICY CONCEPTS
    +
    +Scope of Net Policies
    +
    + Device net policy: this policy applies to the whole device. Once the
    + device net policy is set, it automatically configures the system
    + according to the applied policy. The configuration usually includes IRQ
    + affinity, IRQ balance disable, interrupt moderation, and so on. But the
    + device net policy does not change the packet direction.
    +
    + Task net policy: this is a per-task policy. When it is applied to specific
    + task, all packet transmissions of the task will be redirected to the
    + assigned queues accordingly. If a task does not define a task policy,
    + it "falls back" to the system default way to direct the packets. The
    + per-task policy must be compatible with device net policy.
    +
    + Socket net policy: this is a per-socket policy. When it is applied to
    + specific socket, all packet transmissions of the socket will be redirected
    + to the assigned queues accordingly. If a socket does not define a socket
    + policy, it "falls back" to the system default way to direct the packets.
    + The per-socket policy must be compatible with both device net policy and
    + per-task policy.
    +
    +Components of Net Policies
    +
    + Net policy object: it is a combination of CPU and queue. The queue IRQ has
    + to set affinity with the CPU. It can be shared between sockets and tasks.
    + A reference counter is used to track the sharing number.
    +
    + Net policy object list: each device policy has an object list. Once the
    + device policy is determined, the net policy object will be inserted into
    + the net policy object list. The net policy object list does not change
    + unless the CPU/queue number is changed, the netpolicy is disabled or
    + the device policy is changed.
    + The network performance for objects could be different because of the
    + CPU/queue topology and dev location. The objects which can bring high
    + performance are in the front of the list.
    +
    + RCU hash table: an RCU hash table to maintain the relationship between
    + the task/socket and the assigned object. The task/socket can get the
    + assigned object by searching the table.
    + If it is the first time, there is no assigned object in the table. It will
    + go through the object list to find the available object based on position
    + and reference number.
    + If the net policy object list changes, all the assigned objects will become
    + invalid.
    +
    +NET POLICY APIs
    +
    +Interfaces between net policy and device driver
    +
    + int (*ndo_netpolicy_init)(struct net_device *dev,
    + struct netpolicy_info *info);
    +
    + The device driver who has NET policy support must implement this interface.
    + In this interface, the device driver does necessory initialization, and fill
    + the info for net policy module. The information could include supported
    + policy, MIX policy support, queue pair support and so on.
    +
    + int (*ndo_get_irq_info)(struct net_device *dev,
    + struct netpolicy_dev_info *info);
    +
    + This interface is used to get more accurate device IRQ information.
    +
    + int (*ndo_set_net_policy)(struct net_device *dev,
    + enum netpolicy_name name);
    +
    + This interface is used to set device net policy by name. It is device driver's
    + responsibility to set driver specific configuration for the given policy.
    +
    +Interfaces between net policy and kernel
    +
    + int netpolicy_register(struct netpolicy_instance *instance);
    + void netpolicy_unregister(struct netpolicy_instance *instance);
    +
    + This interface is used to register per task/socket net policy.
    + The socket/task can only be benefited when it register itself with specific
    + policy. After registeration, a record will be created and inserted into RCU
    + hash table, which include all the NET policy related information for the
    + socket/task, such as pointor, policy, object and so on.
    +
    + int netpolicy_pick_queue(struct netpolicy_instance *instance, bool is_rx);
    +
    + This interface is used to find the proper queue(object) for packet
    + receiving and transmitting. The proper queue is picked from object list
    + according to policy, reference, location and so on.
    +
    +
    + int netpolicy_set_rules(struct netpolicy_instance *instance);
    +
    + This interface is used to add device specific rules. Once the rule is
    + applied, the packet from specific IP and port will be redirected to the
    + given queue. This interface is usually used on receive side.
    +
    +NET POLICY INTERFACE
    +
    +Device net policy setting
    +
    + /proc/net/netpolicy/$DEV/policy
    +
    + Concatenating(cat) the "policy" file can show the available device
    + policies, if there is no device policy applied. Otherwise, the device
    + policy name will be printed out. If it is MIX policy, the policy for each
    + queue will also be printed out.
    + User can set device net policy by writing policy name.
    +
    +Task policy setting
    +
    + /proc/$PID/net_policy
    +
    + Concatenating(cat) the "net_policy" file can show the applied per task
    + policy.
    + User can set per task net policy by writing policy name.
    +
    + OR
    +
    + prctl(PR_SET_NETPOLICY, POLICY_NAME, NULL, NULL, NULL)
    +
    + "prctl" is an alternative way to set/get per task policy.
    +
    +Socket policy setting
    +
    + setsockopt(sockfd,SOL_SOCKET,SO_NETPOLICY,&policy,sizeof(int))
    +
    + The socket net policy can be set by option SO_NETPOLICY of setsockopt.
    +
    +AVAILABLE NET POLICIES
    +
    + The available net policies are defined as below:
    + - CPU: intends to get higher throughput and lower CPU% (power saving).
    + This policy can be applied as either device net policy or
    + task/socket net policy.
    + - BULK: intends to get highest throughput. This policy can be applied as
    + either device net policy or task/socket net policy.
    + - LATENCY: intends to get lowest latency. This policy can be applied as
    + either device net policy or task/socket net policy.
    + - MIX: combination of other policies, which allows each queue to have a
    + different policy. This policy can only be set as device net policy.
    +
    --
    2.5.5
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