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Add documentation for HWC in nOS-V

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Rodrigo Arias 2025-09-08 14:41:53 +02:00
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doc/user/emulation/nosv.md
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@ -104,3 +104,32 @@ of CPUs in that state, not the physical CPUs like other views.
Here is an example of the Heat mini-app:
![Breakdown example](fig/breakdown-nosv.png)
## Hardware counters (HWC) view
The hardware counter view allows you to see the *delta* of a given set of
hardware counters over time. The counters are read at the beginning and end of
tasks as well as at some nOS-V API methods.
To enable support for HWC in nOS-V use at least level 2 in `ovni.level` or
enable the "hwc" event set in nosv.toml. Then, make sure the
`hwcounters.backend` option is set to "papi" and select the counters you want to
enable in `hwcounters.papi_events`. Here is an example to trace total
instructions and cycles:
```
instrumentation.version = "ovni"
ovni.level = 2
hwcounters.backend = "papi"
hwcounters.papi_events = [ "PAPI_TOT_INS", "PAPI_TOT_CYC" ]
```
You can use the `papi_avail` tool to see which counters are available for a
particular machine and a description of each counter. Each CPU has a limit in
how many counters can be enabled at the same time, reported in the *Number
Hardware Counters* line.
The events for HWC are generated in cpu.prv and thread.prv for CPUs and threads,
respectively. For each enabled hardware counter, a new configuration file will
be created at `cfg/cpu/nosv/hwc-*.cfg` and `cfg/thread/nosv/hwc-*.cfg` with the
corresponding name of the counter.