On 7/17/15 6:02 PM, pi3orama wrote:
An example: we want to count the number of cycles between entry and exit point
of a particular library function (glibc write() for example). Context switch is
possible, but we don't care cycles consumed by other tasks. Then we need to
create a perf event in task context using:
perf _event_open(&attr, pid, -1/* cpu */, ...);
Since it is a library function, we have to choose pids we interest.
sure. just store that fd under whatever index in perf_event_array
and use it from the program. index is not cpuid. it's just an index.
We should also probe sys_clone and create new perf event when thread creating,
we haven't think how to do that now.
opening a perf_event from the program? That will be very very hard.
Much easier to kprobe sys_clone and signal to user space via
bpf_output_trace_data() and user space will be
perf_event_open-ing new event for new task.
ps
please tweak your email client to wrap lines.
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