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authorJesse Brandeburg <jesse.brandeburg@intel.com>2006-11-01 08:48:13 -0800
committerJeff Garzik <jeff@garzik.org>2006-12-02 00:12:00 -0500
commit835bb1298311f372a3387fb40b952b18d90aa9f8 (patch)
tree1a58003158f03397212979727c2f5cfa37ebc4f2 /Documentation
parent9ac98284428961bd5be285a6cc1f5e6f5b6644aa (diff)
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e1000: add dynamic itr modes
Add a new dynamic itr algorithm, with 2 modes, and make it the default operation mode. This greatly reduces latency and increases small packet performance, at the "cost" of some CPU utilization. Bulk traffic throughput is unaffected. The driver can limit the amount of interrupts per second that the adapter will generate for incoming packets. It does this by writing a value to the adapter that is based on the maximum amount of interrupts that the adapter will generate per second. Setting InterruptThrottleRate to a value greater or equal to 100 will program the adapter to send out a maximum of that many interrupts per second, even if more packets have come in. This reduces interrupt load on the system and can lower CPU utilization under heavy load, but will increase latency as packets are not processed as quickly. The default behaviour of the driver previously assumed a static InterruptThrottleRate value of 8000, providing a good fallback value for all traffic types,but lacking in small packet performance and latency. The hardware can handle many more small packets per second however, and for this reason an adaptive interrupt moderation algorithm was implemented. Since 7.3.x, the driver has two adaptive modes (setting 1 or 3) in which it dynamically adjusts the InterruptThrottleRate value based on the traffic that it receives. After determining the type of incoming traffic in the last timeframe, it will adjust the InterruptThrottleRate to an appropriate value for that traffic. The algorithm classifies the incoming traffic every interval into classes. Once the class is determined, the InterruptThrottleRate value is adjusted to suit that traffic type the best. There are three classes defined: "Bulk traffic", for large amounts of packets of normal size; "Low latency", for small amounts of traffic and/or a significant percentage of small packets; and "Lowest latency", for almost completely small packets or minimal traffic. In dynamic conservative mode, the InterruptThrottleRate value is set to 4000 for traffic that falls in class "Bulk traffic". If traffic falls in the "Low latency" or "Lowest latency" class, the InterruptThrottleRate is increased stepwise to 20000. This default mode is suitable for most applications. For situations where low latency is vital such as cluster or grid computing, the algorithm can reduce latency even more when InterruptThrottleRate is set to mode 1. In this mode, which operates the same as mode 3, the InterruptThrottleRate will be increased stepwise to 70000 for traffic in class "Lowest latency". Setting InterruptThrottleRate to 0 turns off any interrupt moderation and may improve small packet latency, but is generally not suitable for bulk throughput traffic. Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com> Cc: Rick Jones <rick.jones2@hp.com> Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
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