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diff --git a/Documentation/networking/net_dim.txt b/Documentation/networking/net_dim.txt deleted file mode 100644 index 9bdb7d5a3ba3..000000000000 --- a/Documentation/networking/net_dim.txt +++ /dev/null @@ -1,174 +0,0 @@ -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); - ... -} |