Re: new static user probe types

[Stan Cox <scox@redhat.com>]

The performance for the respective static probe types, for a test 
program that invokes a static user probe in a loop 1,000,000 times, is:
kprobe 1.61user 4.73system
utrace 1.38user 22.02system
uprobe 1.24user 11.30system

It ended up that the guard statements in the probes were too permissive; 
fixing this and doing some guard statement performance tweaks yields:
kprobe 1.65user 3.78system
utrace 1.19user 6.03system
uprobe 1.24user 11.30system

The guard statements this experiments is using look like:
kprobe:
if ((task_tid(task_current())) != (_utrace_syscall_arg(1))) next   # 
current task?
if ((pointer_arg(1)) != (_stp_probe_name_test)) {      # probe name ptr 
differs from saved?
if ((user_int(pointer_arg(1))) != (1953719668)) next  # check first word 
of probe name
if ((user_string(pointer_arg(1))) != ("test")) next       # check string 
if all else fails
}
(_stp_probe_name_test) = (pointer_arg(1))               # remember saved 
probe name ptr

utrace:
if ((_utrace_syscall_nr()) != (48813)) next               # is this the 
fake sdt "syscall"
if ((pointer_arg(1)...                                               # 
as above

Running oprofile:
kprobe old 27% strlcpy 11% int3
          exp 13% __ticket_spin_lock 10% int3
utrace old  25% search_extable 18% page_fault 16% strlcpy
         exp  43% start_callback 5% system_call