PMC based Performance Measurement in FreeBSD |
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This is a performance measurement framework for FreeBSD which uses the hardware performance measurement counters in modern CPUs to provide low-overhead, non-intrusive, system-wide measurement of production systems.
Some parts of this work are present in FreeBSD 6.0 and later. Development of new features is happening in -CURRENT.
Alert: I'm currently looking for sponsors for PmcTools work. Please contact me if you would like to help support my work.
These pages are being slowly moved over to the FreeBSD wiki at http://wiki.FreeBSD.org/PmcTools. Please check there too for information and updates.
| Feature | Status | Description |
|---|---|---|
| SMP support? | Ready | Supports profiling on multi-processor systems. |
| System-wide event counting? | Ready | Allows you to get a global view of the events happening on hardware as the system runs. |
| System-wide statistical sampling? | Ready | Allows you to profile userland and kernel (including interrupt handlers) at the same time. |
| Process-"virtual" PMCs? | Ready | Measure hardware events seen by the system when specific processes are scheduled on the CPU(s). |
| Profiling "kernel threads" | Ready | Allows you to profile specific kernel threads. |
| Profiling threaded code | Needs testing. | Allows you to profile threaded applications. |
| Profiling of loadable kernel modules and dlopen() libraries | Ready. | Allows dynamically loaded objects (in the kernel or in userland) to be profiled. |
| Allow perfmon instructions like RDPMC? | Ready | Allows processes that allocated and attached PMCs to themselves to use low-overhead machine instructions to read their PMCs. |
| Simultaneous process-virtual and system-wide profiling? | Ready | Allows you to get a bird-eye view of system-wide hot-spots and drill down further into troublesome processes. |
| Multiple processes using PMCs at the same time? | Ready | The hwpmc(4) driver multiplexes available PMC resources, allowing multiple PMC-using processes to be executing concurrently. |
| Works on stock (i.e., optimized) binaries? | Ready | You can do basic profiling on stock binaries. |
| Callgraphs? | Under design | An oft-requested feature. |
| Integration with system profiling tools gprof(1), kgmon(8)? | In progress. | You can use gprof(1) for your analyses, for now. |
| Cross-architecture PMC API? | Ready | See pmc(3). |
| Remote logging? | Ready | Profile logs can be collected and analysed on a different system; allows for profiling embedded systems. |
| Low-overhead? | Partially characterized | Target: less than 5% processor overhead when active. Negligible overhead when present but turned off. We appear to be on target for most workloads. |
| Supports all PMCs on CPUs running FreeBSD's Tier-1&2 architectures? | Partially there | Currently the following PMCs are supported: AMD64 "K8", AMD Athlon XP "K7", Intel P-Pro/P-II/P-III/Celeron/Pentium-M, Intel P4(HTT). Intel Pentium/MMX support is planned shortly (if I can get -CURRENT to run on it). |
| GUI Analysis tools? | Planned | Help wanted! PAPI interface, spiffy GUI viewers are desired. |
| Documentation | In progress | Manual pages: for the library pmc(3), driver hwpmc(4) and the administrative tools pmcstat(8), pmccontrol(8). A tutorial on using the pmc(3) API is also in progress. |
| Test-suite? | Planned. | A test suite for pmc(3) and hwpmc(4) is planned. |
| Scripting language API? | In progress | A Python wrapper around pmc(3) is being written. |
| Item | State | Description |
|---|---|---|
| Kernel Module [hwpmc(4)] | Done |
Implementations are available for AMD Athlon XP, AMD Athlon 64, Intel P4/HTT and Intel P-Pro/P-II/P-III class CPUs. |
| Programming API [pmc(3)] | Done |
An API to access the facilities offered by hwpmc(4). |
| pmccontrol(8) | Done. |
Administrative control of the hwpmc(4) driver. |
| pmcstat(8) | Done. |
Performance measurements using hwpmc(4). |
| Python Wrapper | Available | A Python Wrapper for pmc(3). A wrapper for pmclog(3) is under development. |
| Test Suite | In Design | A regression test suite for pmc(3) and hwpmc(4). |
| PAPI interface | In design |
How the machine-dependent layer of the PAPI library will interface with this subsystem. |
| Log file format | Done |
This is the format of the log file generated by hwpmc(4). A set of parser routines ( pmclog_* ) for the format is present in pmclog(3). |
| A reporting tool equivalent to gprof(1) | Done |
Use pmcstat(8) -g to generate gprof compatible flat profiles. |
| AMD x86-64 Support | Done |
AMD64 now has 'first-class' support. |
| Alpha/PPC/Sparc64/IA-64/Other Support | Desired | I don't have access to these machines. If you want to see these implemented please consider loaning hardware. |
The system has the following parts (Figure 1):
Key:
There are many projects similar to this one. These are listed on a separate page.
I would like to gratefully acknowledge the help and encouragement from my friends in this project:
| Contact: jkoshy@FreeBSD.org |
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