On Wed, Mar 21, 2018 at 12:44:29PM -0700, Florian Fainelli wrote: > On 03/21/2018 12:37 PM, Randy Dunlap wrote: > > On 03/21/2018 11:33 AM, Tal Gilboa wrote: > >> Net DIM is a generic algorithm, purposed for dynamically > >> optimizing network devices interrupt moderation. This > >> document describes how it works and how to use it. > >> > >> Signed-off-by: Tal Gilboa <ta...@mellanox.com> > >> --- > >> Documentation/networking/net_dim.txt | 174 > >> +++++++++++++++++++++++++++++++++++ > >> 1 file changed, 174 insertions(+) > >> create mode 100644 Documentation/networking/net_dim.txt > >> > >> diff --git a/Documentation/networking/net_dim.txt > >> b/Documentation/networking/net_dim.txt > >> new file mode 100644 > >> index 0000000..9cb31c5 > >> --- /dev/null > >> +++ b/Documentation/networking/net_dim.txt > >> @@ -0,0 +1,174 @@ > >> +Net DIM - Generic Network Dynamic Interrupt Moderation > >> +====================================================== > >> + > >> +Author: > >> + Tal Gilboa <ta...@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. > > > > I think a short description of the predefined profiles could help. > > Agreed it would help if the different modes > (NET_DIM_CQ_PERIOD_MODE_START_FROM_EQE, > NET_DIM_CQ_PERIOD_MODE_START_FROM_CQE) were expanded a bit further. The
Speaking of these, I just had to edit the email and adjust the alignment to notice the single letter difference between both out of 36 chars. NET_DIM_CQ_PERIOD_MODE_START_FROM_EQE NET_DIM_CQ_PERIOD_MODE_START_FROM_CQE Would be nice if the readability could be improved somehow. > whole term QE sounds very much Ethernet converged adapter to me... >
