c - What are the best to ways measure latencies from user space to kernel space? -


i have measure latency between user space program driver interacts with. send packet through application. latecny between write in user space corresponding write function in kernel

i used clock_gettime clock_monotonic in user space , getrawmonotonic in kernel (driver) , when see difference, huge (around 4ms). using wrong approach.

so, best ways this?

to measure single context switch user- kernel-space, try use tsc (time stamp counter). available on x86 , arms, user- , kernel-space.

more info tsc on wikipedia: https://en.wikipedia.org/wiki/time_stamp_counter

bsd-licensed implementation x86 could found here , for 64-bit arm here.

also, comments suggested, consider use standard tool available measure round-trip latency, i.e. use-to-kernel , back.


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