z8530book
msg_zerocopy
failover
+ net_dim
net_failover
phy
sfp-phylink
--- /dev/null
+======================================================
+Net DIM - Generic Network Dynamic Interrupt Moderation
+======================================================
+
+:Author: Tal Gilboa <talgi@mellanox.com>
+
+.. contents:: :depth: 2
+
+Assumptions
+===========
+
+This document assumes the reader has basic knowledge in network drivers
+and in general interrupt moderation.
+
+
+Introduction
+============
+
+Dynamic Interrupt Moderation (DIM) (in networking) refers to changing the
+interrupt moderation configuration of a channel in order to optimize packet
+processing. The mechanism includes an algorithm which decides if and how to
+change moderation parameters for a channel, usually by performing an analysis on
+runtime data sampled from the system. Net DIM is such a mechanism. In each
+iteration of the algorithm, it analyses a given sample of the data, compares it
+to the previous sample and if required, it can decide to change some of the
+interrupt moderation configuration fields. The data sample is composed of data
+bandwidth, the number of packets and the number of events. The time between
+samples is also measured. Net DIM compares the current and the previous data and
+returns an adjusted interrupt moderation configuration object. In some cases,
+the algorithm might decide not to change anything. The configuration fields are
+the minimum duration (microseconds) allowed between events and the maximum
+number of wanted packets per event. The Net DIM algorithm ascribes importance to
+increase bandwidth over reducing interrupt rate.
+
+
+Net DIM Algorithm
+=================
+
+Each iteration of the Net DIM algorithm follows these steps:
+
+#. Calculates new data sample.
+#. Compares it to previous sample.
+#. Makes a decision - suggests interrupt moderation configuration fields.
+#. Applies a schedule work function, which applies suggested configuration.
+
+The first two steps are straightforward, both the new and the previous data are
+supplied by the driver registered to Net DIM. The previous data is the new data
+supplied to the previous iteration. The comparison step checks the difference
+between the new and previous data and decides on the result of the last step.
+A step would result as "better" if bandwidth increases and as "worse" if
+bandwidth reduces. If there is no change in bandwidth, the packet rate is
+compared in a similar fashion - increase == "better" and decrease == "worse".
+In case there is no change in the packet rate as well, the interrupt rate is
+compared. Here the algorithm tries to optimize for lower interrupt rate so an
+increase in the interrupt rate is considered "worse" and a decrease is
+considered "better". Step #2 has an optimization for avoiding false results: it
+only considers a difference between samples as valid if it is greater than a
+certain percentage. Also, since Net DIM does not measure anything by itself, it
+assumes the data provided by the driver is valid.
+
+Step #3 decides on the suggested configuration based on the result from step #2
+and the internal state of the algorithm. The states reflect the "direction" of
+the algorithm: is it going left (reducing moderation), right (increasing
+moderation) or standing still. Another optimization is that if a decision
+to stay still is made multiple times, the interval between iterations of the
+algorithm would increase in order to reduce calculation overhead. Also, after
+"parking" on one of the most left or most right decisions, the algorithm may
+decide to verify this decision by taking a step in the other direction. This is
+done in order to avoid getting stuck in a "deep sleep" scenario. Once a
+decision is made, an interrupt moderation configuration is selected from
+the predefined profiles.
+
+The last step is to notify the registered driver that it should apply the
+suggested configuration. This is done by scheduling a work function, defined by
+the Net DIM API and provided by the registered driver.
+
+As you can see, Net DIM itself does not actively interact with the system. It
+would have trouble making the correct decisions if the wrong data is supplied to
+it and it would be useless if the work function would not apply the suggested
+configuration. This does, however, allow the registered driver some room for
+manoeuvre as it may provide partial data or ignore the algorithm suggestion
+under some conditions.
+
+
+Registering a Network Device to DIM
+===================================
+
+Net DIM API exposes the main function net_dim().
+This function is the entry point to the Net
+DIM algorithm and has to be called every time the driver would like to check if
+it should change interrupt moderation parameters. The driver should provide two
+data structures: :c:type:`struct dim <dim>` and
+:c:type:`struct dim_sample <dim_sample>`. :c:type:`struct dim <dim>`
+describes the state of DIM for a specific object (RX queue, TX queue,
+other queues, etc.). This includes the current selected profile, previous data
+samples, the callback function provided by the driver and more.
+:c:type:`struct dim_sample <dim_sample>` describes a data sample,
+which will be compared to the data sample stored in :c:type:`struct dim <dim>`
+in order to decide on the algorithm's next
+step. The sample should include bytes, packets and interrupts, measured by
+the driver.
+
+In order to use Net DIM from a networking driver, the driver needs to call the
+main net_dim() function. The recommended method is to call net_dim() on each
+interrupt. Since Net DIM has a built-in moderation and it might decide to skip
+iterations under certain conditions, there is no need to moderate the net_dim()
+calls as well. As mentioned above, the driver needs to provide an object of type
+:c:type:`struct dim <dim>` to the net_dim() function call. It is advised for
+each entity using Net DIM to hold a :c:type:`struct dim <dim>` as part of its
+data structure and use it as the main Net DIM API object.
+The :c:type:`struct dim_sample <dim_sample>` should hold the latest
+bytes, packets and interrupts count. No need to perform any calculations, just
+include the raw data.
+
+The net_dim() call itself does not return anything. Instead Net DIM relies on
+the driver to provide a callback function, which is called when the algorithm
+decides to make a change in the interrupt moderation parameters. This callback
+will be scheduled and run in a separate thread in order not to add overhead to
+the data flow. After the work is done, Net DIM algorithm needs to be set to
+the proper state in order to move to the next iteration.
+
+
+Example
+=======
+
+The following code demonstrates how to register a driver to Net DIM. The actual
+usage is not complete but it should make the outline of the usage clear.
+
+.. code-block:: c
+
+ #include <linux/dim.h>
+
+ /* Callback for net DIM to schedule on a decision to change moderation */
+ void my_driver_do_dim_work(struct work_struct *work)
+ {
+ /* Get struct dim from struct work_struct */
+ struct dim *dim = container_of(work, struct dim,
+ work);
+ /* Do interrupt moderation related stuff */
+ ...
+
+ /* Signal net DIM work is done and it should move to next iteration */
+ dim->state = DIM_START_MEASURE;
+ }
+
+ /* My driver's interrupt handler */
+ int my_driver_handle_interrupt(struct my_driver_entity *my_entity, ...)
+ {
+ ...
+ /* A struct to hold current measured data */
+ struct dim_sample dim_sample;
+ ...
+ /* Initiate data sample struct with current data */
+ dim_update_sample(my_entity->events,
+ my_entity->packets,
+ my_entity->bytes,
+ &dim_sample);
+ /* Call net DIM */
+ net_dim(&my_entity->dim, dim_sample);
+ ...
+ }
+
+ /* My entity's initialization function (my_entity was already allocated) */
+ int my_driver_init_my_entity(struct my_driver_entity *my_entity, ...)
+ {
+ ...
+ /* Initiate struct work_struct with my driver's callback function */
+ INIT_WORK(&my_entity->dim.work, my_driver_do_dim_work);
+ ...
+ }
+++ /dev/null
-Net DIM - Generic Network Dynamic Interrupt Moderation
-======================================================
-
-Author:
- Tal Gilboa <talgi@mellanox.com>
-
-
-Contents
-=========
-
-- Assumptions
-- Introduction
-- The Net DIM Algorithm
-- Registering a Network Device to DIM
-- Example
-
-Part 0: Assumptions
-======================
-
-This document assumes the reader has basic knowledge in network drivers
-and in general interrupt moderation.
-
-
-Part I: Introduction
-======================
-
-Dynamic Interrupt Moderation (DIM) (in networking) refers to changing the
-interrupt moderation configuration of a channel in order to optimize packet
-processing. The mechanism includes an algorithm which decides if and how to
-change moderation parameters for a channel, usually by performing an analysis on
-runtime data sampled from the system. Net DIM is such a mechanism. In each
-iteration of the algorithm, it analyses a given sample of the data, compares it
-to the previous sample and if required, it can decide to change some of the
-interrupt moderation configuration fields. The data sample is composed of data
-bandwidth, the number of packets and the number of events. The time between
-samples is also measured. Net DIM compares the current and the previous data and
-returns an adjusted interrupt moderation configuration object. In some cases,
-the algorithm might decide not to change anything. The configuration fields are
-the minimum duration (microseconds) allowed between events and the maximum
-number of wanted packets per event. The Net DIM algorithm ascribes importance to
-increase bandwidth over reducing interrupt rate.
-
-
-Part II: The Net DIM Algorithm
-===============================
-
-Each iteration of the Net DIM algorithm follows these steps:
-1. Calculates new data sample.
-2. Compares it to previous sample.
-3. Makes a decision - suggests interrupt moderation configuration fields.
-4. Applies a schedule work function, which applies suggested configuration.
-
-The first two steps are straightforward, both the new and the previous data are
-supplied by the driver registered to Net DIM. The previous data is the new data
-supplied to the previous iteration. The comparison step checks the difference
-between the new and previous data and decides on the result of the last step.
-A step would result as "better" if bandwidth increases and as "worse" if
-bandwidth reduces. If there is no change in bandwidth, the packet rate is
-compared in a similar fashion - increase == "better" and decrease == "worse".
-In case there is no change in the packet rate as well, the interrupt rate is
-compared. Here the algorithm tries to optimize for lower interrupt rate so an
-increase in the interrupt rate is considered "worse" and a decrease is
-considered "better". Step #2 has an optimization for avoiding false results: it
-only considers a difference between samples as valid if it is greater than a
-certain percentage. Also, since Net DIM does not measure anything by itself, it
-assumes the data provided by the driver is valid.
-
-Step #3 decides on the suggested configuration based on the result from step #2
-and the internal state of the algorithm. The states reflect the "direction" of
-the algorithm: is it going left (reducing moderation), right (increasing
-moderation) or standing still. Another optimization is that if a decision
-to stay still is made multiple times, the interval between iterations of the
-algorithm would increase in order to reduce calculation overhead. Also, after
-"parking" on one of the most left or most right decisions, the algorithm may
-decide to verify this decision by taking a step in the other direction. This is
-done in order to avoid getting stuck in a "deep sleep" scenario. Once a
-decision is made, an interrupt moderation configuration is selected from
-the predefined profiles.
-
-The last step is to notify the registered driver that it should apply the
-suggested configuration. This is done by scheduling a work function, defined by
-the Net DIM API and provided by the registered driver.
-
-As you can see, Net DIM itself does not actively interact with the system. It
-would have trouble making the correct decisions if the wrong data is supplied to
-it and it would be useless if the work function would not apply the suggested
-configuration. This does, however, allow the registered driver some room for
-manoeuvre as it may provide partial data or ignore the algorithm suggestion
-under some conditions.
-
-
-Part III: Registering a Network Device to DIM
-==============================================
-
-Net DIM API exposes the main function net_dim(struct dim *dim,
-struct dim_sample end_sample). This function is the entry point to the Net
-DIM algorithm and has to be called every time the driver would like to check if
-it should change interrupt moderation parameters. The driver should provide two
-data structures: struct dim and struct dim_sample. Struct dim
-describes the state of DIM for a specific object (RX queue, TX queue,
-other queues, etc.). This includes the current selected profile, previous data
-samples, the callback function provided by the driver and more.
-Struct dim_sample describes a data sample, which will be compared to the
-data sample stored in struct dim in order to decide on the algorithm's next
-step. The sample should include bytes, packets and interrupts, measured by
-the driver.
-
-In order to use Net DIM from a networking driver, the driver needs to call the
-main net_dim() function. The recommended method is to call net_dim() on each
-interrupt. Since Net DIM has a built-in moderation and it might decide to skip
-iterations under certain conditions, there is no need to moderate the net_dim()
-calls as well. As mentioned above, the driver needs to provide an object of type
-struct dim to the net_dim() function call. It is advised for each entity
-using Net DIM to hold a struct dim as part of its data structure and use it
-as the main Net DIM API object. The struct dim_sample should hold the latest
-bytes, packets and interrupts count. No need to perform any calculations, just
-include the raw data.
-
-The net_dim() call itself does not return anything. Instead Net DIM relies on
-the driver to provide a callback function, which is called when the algorithm
-decides to make a change in the interrupt moderation parameters. This callback
-will be scheduled and run in a separate thread in order not to add overhead to
-the data flow. After the work is done, Net DIM algorithm needs to be set to
-the proper state in order to move to the next iteration.
-
-
-Part IV: Example
-=================
-
-The following code demonstrates how to register a driver to Net DIM. The actual
-usage is not complete but it should make the outline of the usage clear.
-
-my_driver.c:
-
-#include <linux/dim.h>
-
-/* Callback for net DIM to schedule on a decision to change moderation */
-void my_driver_do_dim_work(struct work_struct *work)
-{
- /* Get struct dim from struct work_struct */
- struct dim *dim = container_of(work, struct dim,
- work);
- /* Do interrupt moderation related stuff */
- ...
-
- /* Signal net DIM work is done and it should move to next iteration */
- dim->state = DIM_START_MEASURE;
-}
-
-/* My driver's interrupt handler */
-int my_driver_handle_interrupt(struct my_driver_entity *my_entity, ...)
-{
- ...
- /* A struct to hold current measured data */
- struct dim_sample dim_sample;
- ...
- /* Initiate data sample struct with current data */
- dim_update_sample(my_entity->events,
- my_entity->packets,
- my_entity->bytes,
- &dim_sample);
- /* Call net DIM */
- net_dim(&my_entity->dim, dim_sample);
- ...
-}
-
-/* My entity's initialization function (my_entity was already allocated) */
-int my_driver_init_my_entity(struct my_driver_entity *my_entity, ...)
-{
- ...
- /* Initiate struct work_struct with my driver's callback function */
- INIT_WORK(&my_entity->dim.work, my_driver_do_dim_work);
- ...
-}
S: Maintained
F: include/linux/dim.h
F: lib/dim/
+F: Documentation/networking/net_dim.rst
DZ DECSTATION DZ11 SERIAL DRIVER
M: "Maciej W. Rozycki" <macro@linux-mips.org>
projects / kernel.git / commitdiff