Hi, On Sun, Sep 13, 2009 at 8:35 PM, Godmar Back<god...@gmail.com> wrote: > Date: September 13, 2009 > > Stephane, > > I have a few questions about perfmon2. First off, I apologize for not > having read the source code; I'm certain that the answers to at least > some of these questions are contained in it. Still, it may be helpful > to create a record online to help others better understand where > perfmon2 stands at this point. > > I read your 20-month old presentation at > http://perfmon2.sourceforge.net/perfmon2-20080124.pdf > > Q1: Is there a newer document available that describes perfmon2? > No, that is the most recent document. Not much has changed in the API since then.
> Q2: The presentation states that Perfmon2 is to become "the Linux > monitoring interface." Has this become true? > No. In fact perfmon2 has been rejected in favor of a new API called perf_counters. This new API is now in 2.6.31 (for X86 only). > Q3: Just looking at provided functionality, and ignoring support by > higher-level tools, would perfmon2 have the ability to replace the > perfctr library and kernel patch? > Yes. It does provide the same functionalities. > Q4: Can perfmon2 replace the Intel Vtune driver, just based on functionality? > Both tools use system-wide monitoring. Perfmon2 does provide system-wide counting and sampling, so I believe with little work support for those tools would be possible. > Q5: Does perfmon2 support direct access to virtualized performance > counter registers in user mode in the manner perfctr does? Slides 16 > and 27 appear to imply that. In perfctr, such access is supported by > allowing a thread read-only access from user mode to the state > container structure into which the context switch code saved those > registers. Does perfmon2 support a similar approach, or do all > accesses to performance counter registers require a system call? > If by virtualized you mean that perfmon2 allows per-thread monitoring, then the answer is yes. You can attach a monitoring session to a thread. As the thread is context switched in and out, the monitoring session (PMU state) is also saved and restored. Counts specific to that thread can be extracted via a system call. At some point, perfmon2 also had the ability to read the counts directly from user-space using a remapping trick. But that was abandoned to simplify the code. But the same trick perfctr uses could also be used. > Q6: Slides 32-34 list tools supporting perfmon2. Notably absent are > the two major vendor tools Intel's VTune and AMD's Code Analyst. The > former uses their own driver, and the latter relies on perfctr (to my > knowledge). What is known about support for perfmon2 in these > products? > None do support perfmon2 at this point. > Q7: The slides discuss that perfmon2 support is slated for inclusion > into commercial Linux distributions. Are there already any commercial > Linux distribution that have perfmon2 support in their kernels? If > so, which ones? > Yes, All Itanium-based distributions includes an earlier version of perfmon2 called v2.0. I believe SLES11 on x86 may have perfmon2. > Q8: Slide 6 points out that performance counters may need to be > accessed in virtualized environments. What support, if any, does > perfmon2 provide for accessing performance counters as of now? None at this point unfortunately. > Specifically, is it possible to use perfmon2 in a Xen/Guest kernel; if > not, is anybody working on adding such support? What about KVM? > To my knowledge, I don't believe it is possible to transparently access the performance counters from within a guest in Xen. I know of XenOprofile but this is a modified guest. As for KVM, I think the situation is similar. ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
