Messages in this thread | | | Subject | KPROBES: Instrumenting a function's call site | From | Avishay Traeger <> | Date | Tue, 25 Sep 2007 18:12:38 -0400 |
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Hello, I am trying to use kprobes to measure the latency of a function by instrumenting its call site. Basically, I find the call instruction, and insert a kprobe with a pre-handler and post-handler at that point. The pre-handler measures the latency (reads the TSC counter). The post-handler measures the latency again, and subtracts the value that was read in the pre-handler to compute the total latency of the called function.
So to measure the latency of foo(), I basically want kprobes to do this: pre_handler(); foo(); post_handler();
The problem is that the latencies that I am getting are consistently low (~10,000 cycles). When I manually instrument the functions, the latency is about 20,000,000 cycles. Clearly something is not right here.
Is this a known issue? Instead of using the post-handler, I can try to add a kprobe to the following instruction with a pre-handler. I was just curious if there was something fundamentally wrong with the approach I took, or maybe a bug that you should be made aware of.
Please CC me on any replies (not subscribed to LKML).
Thanks, Avishay
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