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Re: user-space probes -- plan B from outer space
jkenisto wrote:
> [...] I was thinking a user-mode (instrumentation) program + a
> kernel module that defines handlers that could be invoked from the
> instrumentation program. The latter (which requires kernel
> enhancements) is necessary only for convenient & efficient
> coordination of user-space and kernel-space instrumentation. [...]
This scheme is more advanced than the hypothetical "plan B", which
would require no kernel changes.
> [...] Yes, pretty slow. In my prototype, my user-mode handler just
> increments a counter. On my Pentium M, overhead per probepoint hit
> is ~14.2 usec, compared with 1.03 usec for the uprobes version last
> posted to LKML. [...]
It would be good to see your code. I'm surprised the slowdown is
*only* a factor of 14.
> My proposed approach to user/kernel data sharing is a new system
> call or ptrace request that just passes a pid, a handler ID, and a
> pointer to an area in user space that the handler (installed via a
> kernel module) can read and/or write. [...]
What would this user space area be used for? If all the handlers run
in kernel space, why not keep all the data there too?
- FChE