Perfmon systemtap runtime support

[William Cohen]

Hi

I have been working on getting some performance monitoring support into 
systemtap. The perfmon1.diff patch is a very simple addition to the 
runtime. It just has functions to setup the perfmon monitoring hardware, 
read a counter, and shutdown the performance monitoring hardware. It 
uses the perfmon2 kernel ABI to configure the hardware.

I have completed changes to the translator to use the runtime functions. 
I took Marin's suggestion of using guru mode to allow access to the 
various C functions and wrote some examples that used the runtime functions.

The cost is relatively high for accessing the counters. Below is the 
output from p2x.stp, counting the number of cycles between consecutive 
calls to read the cycle count:

[wcohen@dhcp59-187 systemtap_perfmon]$ ./install/bin/stap -g  p2x.stp
interval = 15491
[wcohen@dhcp59-187 systemtap_perfmon]$ ./install/bin/stap -g  p2x.stp
interval = 16317
[wcohen@dhcp59-187 systemtap_perfmon]$ ./install/bin/stap -g  p2x.stp
interval = 15431
[wcohen@dhcp59-187 systemtap_perfmon]$ ./install/bin/stap -g  p2x.stp
interval = 15392

I would appreciate any comments or feedback on this code.

-Will
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