On 20/11/2017 08:05, Quan Xu wrote: [ ... ] >>>> But the irq_timings stuff is heading into the same direction, with a >>>> more >>>> complex prediction logic which should tell you pretty good how long >>>> that >>>> idle period is going to be and in case of an interrupt heavy workload >>>> this >>>> would skip the extra work of stopping and restarting the tick and >>>> provide a >>>> very good input into a polling decision. >>> >>> interesting. I have tested with IRQ_TIMINGS related code, which seems >>> not working so far. >> I don't know how you tested it, can you elaborate what you meant by >> "seems not working so far" ? > > Daniel, I tried to enable IRQ_TIMINGS* manually. used > irq_timings_next_event() > to return estimation of the earliest interrupt. However I got a constant. The irq timings gives you an indication of the next interrupt deadline. This information is a piece of the puzzle, you need to combine it with the next timer expiration, and the next scheduling event. Then take the earliest event in a timeline basis. Using the trivial scheme above will work well with workload like videos or mp3 but will fail as soon as the interrupts are not coming in a regular basis and this is where the pattern recognition algorithm must act. >> There are still some work to do to be more efficient. The prediction >> based on the irq timings is all right if the interrupts have a simple >> periodicity. But as soon as there is a pattern, the current code can't >> handle it properly and does bad predictions. >> >> I'm working on a self-learning pattern detection which is too heavy for >> the kernel, and with it we should be able to detect properly the >> patterns and re-ajust the period if it changes. I'm in the process of >> making it suitable for kernel code (both math and perf). >> >> One improvement which can be done right now and which can help you is >> the interrupts rate on the CPU. It is possible to compute it and that >> will give an accurate information for the polling decision. >> >> > As tglx said, talk to each other / work together to make it usable for > all use cases. > could you share how to enable it to get the interrupts rate on the CPU? > I can try it > in cloud scenario. of course, I'd like to work with you to improve it. Sure, I will be glad if we can collaborate. I have some draft code but before sharing it I would like we define what is the rate and what kind of information we expect to infer from it. From my point of view it is a value indicating the interrupt period per CPU, a short value indicates a high number of interrupts on the CPU. This value must decay with the time, the question here is what decay function we apply to the rate from the last timestamp ? -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog
