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Re: syscall tracing overheads: utrace vs. kprobes
Hi -
On Tue, Apr 28, 2009 at 11:10:10AM -0700, Roland McGrath wrote:
> [...]
> The microbenchmark makes that seem like more of a sensical comparison than
> it really is. They are really apples and oranges. The TIF_SYSCALL_TRACE
> types (process.syscall) add some overhead to every system call. The probe
> types (kprobe/tracepoint/marker) add overhead only to the probed call.
Certainly, in general. But in this specific test, only the under-test
system calls occurred in essnetially the whole system, so the overhead
measurements were in a way the bare minimums imposed by the kprobes
vs. utrace callback infrastructure itself.
> In real situations [...] the distribution of overheads will be
> quite different.
Or rather, the basic overhead quanta measured above may be multiplied
along several different axes.
- FChE