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Jul
26
awarded  Autobiographer
Jul
14
comment Reducing Jitter on Ubuntu 15.04 low latency
@DougSmythies That is how I read it. 7% of interrupts are sub jitffy (for a 4000 us jiffy) the rest are either 1x, 2x not more than 3x the jiffy.
Jul
14
comment Reducing Jitter on Ubuntu 15.04 low latency
@DougSmythies You are right it is 100% busy doing something useful but it keeps getting interrupted. If it gets interrupted 85K times or 7K times, it still appears to work which suggests at least 90% of those interrupts are not needed and I suspect something close to 100% are redundant.
Jul
13
revised Reducing Jitter on Ubuntu 15.04 low latency
added 7 characters in body
Jul
13
answered Reducing Jitter on Ubuntu 15.04 low latency
Jul
13
comment Reducing Jitter on Ubuntu 15.04 low latency
@DougSmythies switching from "lowlatency" to "generic" reduced the number of interrupts > 1 us from 85K to 7K over 85 second. Better than a factor of 4.
Jul
13
revised Reducing Jitter on Ubuntu 15.04 low latency
added 615 characters in body
Jul
13
comment Reducing Jitter on Ubuntu 15.04 low latency
@DougSmythies what would happen if the CPU didn't service interrupts at all. e.g. say it was running one thread and not doing anything else.
Jul
13
comment Reducing Jitter on Ubuntu 15.04 low latency
@DougSmythies I was hoping that NO_HZ_FULL and adaptive interrupts wouldn't interrupt a CPU which has only one runnable thread.
Jul
13
comment Reducing Jitter on Ubuntu 15.04 low latency
@DougSmythies I wondered about this. Do you know how to revert the kernel? It appears the generic version was uninstalled when I installed the low latency one.
Jul
13
comment Reducing Jitter on Ubuntu 15.04 low latency
@Daniel I have a fix engine which reads a message, writes the message to as mmap, parses the message, generates a response, writes that to a mmap file and sends the response in ~ 2.5 micro-seconds 85% of the time. This is useful work. However, the kernel interrupts the process for 5 - 10 micro-second delay for no good reason I can work out. It's a bit sad that Java is not the latency outlier but instead it's the kernel.
Jul
13
revised Reducing Jitter on Ubuntu 15.04 low latency
added 113 characters in body
Jul
13
revised Reducing Jitter on Ubuntu 15.04 low latency
added 264 characters in body
Jul
13
revised Reducing Jitter on Ubuntu 15.04 low latency
added 408 characters in body
Jul
13
revised Reducing Jitter on Ubuntu 15.04 low latency
deleted 818 characters in body
Jul
13
revised Reducing Jitter on Ubuntu 15.04 low latency
edited body
Jul
13
revised Reducing Jitter on Ubuntu 15.04 low latency
added 83 characters in body
Jul
13
asked Reducing Jitter on Ubuntu 15.04 low latency
Nov
17
accepted Manual IP configuration disappears
Nov
17
comment Manual IP configuration disappears
Adding the auto line and using ifup worked.