Will, On Tue, Sep 19, 2006 at 04:56:01PM -0400, William Cohen wrote: > > At the very least there needs to be a mechanism to read the values of the > performance monitoring hardware registers in kernel-space. Certainly people > have used get_cycles() to see how long certain things take to do within the > kernel. Having access to the performance monitoring counters would allow > better testing of some hypothesis, e.g. were there fewer or more cache > misses with this approach versus another approach. It isn't practical to do > the read of the performance counter in user-space. Too bad that the > performance hardware designers for most processors took short cuts, so that > a simple direct reading of the perfmon hardware data counters won't work.
ou can read any raw performance counters in kernel space using the appropriate Yassembly instruction. On x86 that would be rdmsr/rdpmc. Of course, that would not give you the full 64-bit (software virtualized) value. But I suspect that in-kernel you are after micro-mesasurements that are unlikely to run long enough to overflow a 32-bit counter (especially if not measuing cycles). I think you are after a small subset of the calls from perfmon2, namely start/stop, read counters. I think the setup/tear-down could be done at the user level, i.e., you'd have to assume there is a session going. If we further assume system-wide ONLY and that you can only operate on the cpu where you issue the call, then it would not be too difficult to add the 3 calls you need. -- -Stephane _______________________________________________ perfmon mailing list [email protected] http://www.hpl.hp.com/hosted/linux/mail-archives/perfmon/
