TheRock/rocm-systems/projects/amdsmi/docs/how-to/amdsmi-cpp-lib.md

---
myst:
  html_meta:
    "description lang=en": "Get started with the AMD SMI C++ library. Basic usage and examples."
    "keywords": "api, smi, lib, c++, system, management, interface, ROCm"
---

# AMD SMI C++ library usage and examples

This section presents a brief overview and some basic examples on the AMD SMI
library's usage. Whether you are developing applications for performance
monitoring, system diagnostics, or resource allocation, the AMD SMI C++ library
serves as a valuable tool for leveraging the full potential of AMD hardware in
your projects.

```{note}
``hipcc`` and other compilers will not automatically link in the ``libamd_smi``
dynamic library. To compile code that uses the AMD SMI library API, ensure the
``libamd_smi.so`` can be located by setting the ``LD_LIBRARY_PATH`` environment
variable to the directory containing ``librocm_smi64.so`` (usually
``/opt/rocm/lib``) or by passing the ``-lamd_smi`` flag to the compiler.
```

```{note}
The following environment variables can be set to control internal cache
durations:

| Variable | Description | Default |
|---|---|---|
| ``AMDSMI_GPU_METRICS_CACHE_MS`` | GPU metrics cache duration (ms) | 1 ms (set to 0 to disable) |
| ``AMDSMI_ASIC_INFO_CACHE_MS`` | GPU ASIC info cache duration (ms) | 10000 ms (set to 0 to disable) |

These can be set in the shell before running your application:

    export AMDSMI_GPU_METRICS_CACHE_MS=200
```

```{seealso}
Refer to the [C/C++ library API reference](../reference/amdsmi-cpp-api/index.md).
```

(device_socket_handle)=
## Device and socket handles

Many functions in the library take a _socket handle_ or _device handle_. A
_socket_ refers to a physical hardware socket, abstracted by the library to
represent the hardware more effectively to the user. While there is always one
unique GPU per socket, an APU may house both a GPU and CPU on the same socket.
For MI200 GPUs, multiple GCDs may reside within a single socket, so a single socket can
own several processor handles. GPU socket IDs are derived from the device's BDF, whereas
CPU socket IDs correspond to the physical CPU package.

To identify the sockets in a system, use the `amdsmi_get_socket_handles()`
function, which returns a list of socket handles. These handles can then be used
with `amdsmi_get_processor_handles()` to query devices within each socket. The
device handle is used to differentiate between detected devices; however, it's
important to note that a device handle may change after restarting the
application, so it should not be considered a persistent identifier across
processes.

The list of socket handles obtained from `amdsmi_get_socket_handles()` can
also be used to query the CPUs in each socket by calling
`amdsmi_get_processor_handles_by_type()`. This function can then be called again
to query the cores within each CPU.

(cpp_hello_amdsmi)=
## Hello AMD SMI

An application using AMD SMI must call `amdsmi_init()` to initialize the AMI SMI
library before all other calls. This call initializes the internal data
structures required for subsequent AMD SMI operations. In the call, a flag can
be passed to indicate if the application is interested in a specific device
type.

`amdsmi_shut_down()` must be the last call to properly close connection to
driver and make sure that any resources held by AMD SMI are released.

1. A simple "Hello World" type program that displays the temperature of detected
   devices.

   ```{note}
   Sample build example:
   $ g++ -I/opt/rocm/include <file_name>.cc -L/opt/rocm/lib -lamd_smi -o <filename>

   Users /opt/rocm-*/bin path may differ (depending on install), please locate the path of your libamd_smi.so.*.
   For example:

   $ sudo find /opt/ -iname libamd_smi.so*
   /opt/rocm-6.4.1/lib/libamd_smi.so.25.0
   /opt/rocm-6.4.1/lib/libamd_smi.so
   ```

   The code is as follows:

   ```cpp
   #include <iostream>
   #include <vector>
   #include "amd_smi/amdsmi.h"

   int main() {
     amdsmi_status_t ret;

     // Init amdsmi for sockets and devices. Here we are only interested in AMD_GPUS.
     ret = amdsmi_init(AMDSMI_INIT_AMD_GPUS);

     // Get all sockets
     uint32_t socket_count = 0;

     // Get the socket count available in the system.
     ret = amdsmi_get_socket_handles(&socket_count, nullptr);

     // Allocate the memory for the sockets
     std::vector<amdsmi_socket_handle> sockets(socket_count);
     // Get the socket handles in the system
     ret = amdsmi_get_socket_handles(&socket_count, &sockets[0]);

     std::cout << "Total Socket: " << socket_count << std::endl;

     // For each socket, get identifier and devices
     for (uint32_t i=0; i < socket_count; i++) {
       // Get Socket info
       char socket_info[128];
       ret = amdsmi_get_socket_info(sockets[i], 128, socket_info);
       std::cout << "Socket " << socket_info<< std::endl;

       // Get the device count for the socket.
       uint32_t device_count = 0;
       ret = amdsmi_get_processor_handles(sockets[i], &device_count, nullptr);

       // Allocate the memory for the device handlers on the socket
       std::vector<amdsmi_processor_handle> processor_handles(device_count);
       // Get all devices of the socket
       ret = amdsmi_get_processor_handles(sockets[i],
                 &device_count, &processor_handles[0]);

       // For each device of the socket, get name and temperature.
       for (uint32_t j=0; j < device_count; j++) {
         // Get device type. Since the amdsmi is initialized with
         // AMD_SMI_INIT_AMD_GPUS, the processor_type must be AMDSMI_PROCESSOR_TYPE_AMD_GPU.
         amdsmi_processor_type_t processor_type;
         ret = amdsmi_get_processor_type(processor_handles[j], &processor_type);
         if (processor_type != AMDSMI_PROCESSOR_TYPE_AMD_GPU) {
           std::cout << "Expect AMDSMI_PROCESSOR_TYPE_AMD_GPU device type!\n";
           return 1;
         }

         // Get device name
         amdsmi_board_info_t board_info;
         ret = amdsmi_get_gpu_board_info(processor_handles[j], &board_info);
         std::cout << "\tdevice "
                     << j <<"\n\t\tName:" << board_info.product_name << std::endl;

         // Get temperature
         int64_t val_i64 = 0;
         ret =  amdsmi_get_temp_metric(processor_handles[j], AMDSMI_TEMPERATURE_TYPE_EDGE,
                 AMDSMI_TEMP_CURRENT, &val_i64);
         std::cout << "\t\tTemperature: " << val_i64 << "C" << std::endl;
       }
     }

     // Clean up resources allocated at amdsmi_init. It will invalidate sockets
     // and devices pointers
     ret = amdsmi_shut_down();

     return 0;
   }
   ```

2. A sample program that displays the power of detected CPUs.

   ```{note}
   Sample build example:
   $ g++ -DENABLE_ESMI -I/opt/rocm/include <file_name>.cc -L/opt/rocm/lib -lamd_smi -o <filename>

   For finding available rocm include and library path, see building example on sample program 1 above.
   ```

   The code is as follows:

   ```cpp
   #include <iostream>
   #include <vector>
   #include "amd_smi/amdsmi.h"

   int main(int argc, char **argv) {
       amdsmi_status_t ret;
       uint32_t socket_count = 0;

       // Initialize amdsmi for AMD CPUs
       ret = amdsmi_init(AMDSMI_INIT_AMD_CPUS);

       ret = amdsmi_get_socket_handles(&socket_count, nullptr);

       // Allocate the memory for the sockets
       std::vector<amdsmi_socket_handle> sockets(socket_count);

       // Get the sockets of the system
       ret = amdsmi_get_socket_handles(&socket_count, &sockets[0]);

       std::cout << "Total Socket: " << socket_count << std::endl;

       // For each socket, get cpus
       for (uint32_t i = 0; i < socket_count; i++) {
           uint32_t cpu_count = 0;

           // Set processor type as AMDSMI_PROCESSOR_TYPE_AMD_CPU
           amdsmi_processor_type_t processor_type = AMDSMI_PROCESSOR_TYPE_AMD_CPU;
           ret = amdsmi_get_processor_handles_by_type(sockets[i], processor_type, nullptr, &cpu_count);

           // Allocate the memory for the cpus
           std::vector<amdsmi_processor_handle> plist(cpu_count);

           // Get the cpus for each socket
           ret = amdsmi_get_processor_handles_by_type(sockets[i], processor_type, &plist[0], &cpu_count);

           for (uint32_t index = 0; index < plist.size(); index++) {
               uint32_t socket_power;
               std::cout<<"CPU "<<index<<"\t"<< std::endl;
               std::cout<<"Power (Watts): ";

               ret = amdsmi_get_cpu_socket_power(plist[index], &socket_power);
               if(ret != AMDSMI_STATUS_SUCCESS)
                   std::cout<<"Failed to get cpu socket power"<<"["<<index<<"] , Err["<<ret<<"] "<< std::endl;

               if (!ret) {
                   std::cout<<static_cast<double>(socket_power)/1000<<std::endl;
               }
               std::cout<<std::endl;
           }
       }

       // Clean up resources allocated at amdsmi_init
       ret = amdsmi_shut_down();

       return 0;
   }
   ```

(multiple_init_perf_opt)=
## Multiple initialization performance optimization

To optimize performance when initializing multiple amd-smi instances, AMD SMI implements a static metrics cache stored
in a Singleton object. This design allows metrics data to persist across multiple instances of amd-smi, whether the
tool is invoked repeatedly or used within a multithreaded C/C++ application. 

Upon creation of the first amd-smi
instance, a Singleton object that contains the metrics cache is instantiated. Any amd-smi instances created thereafter
will inherit the Singleton object metrics cache data. Each amd-smi creation increases the usage counter in the
Singleton object. And each amd-smi destruction decreases the usage counter. When the Singleton counter reaches zero,
the metrics cache is destroyed along with the Singleton object. This principle follows the Singleton Design Principal
of sharing cached data across multiple objects.

```mermaid
graph LR
    subgraph "Singleton Object"
    data_cache["Metrics data cache<br>instances 3"]
    end
    subgraph "amd-smi 1"
    data1[data] ----> data_cache
    end
    subgraph "amd-smi 2"
    data2[data] ----> data_cache
    end
    subgraph "amd-smi 3"
    data3[data] ----> data_cache
    end
```

The data caching can be controlled through two environment variables:
```
AMD_GPU_METRICS_CACHE_MS = 1 ms
AMD_ASIC_INFO_CACHE_MS = 10000 ms
```
These environment variables control how long information is stored in the data cache before it is refreshed.
Therefore calls for the system information will not trigger a system retrieval until the cache goes invalid
and needs refreshing.

(best_practice)=
### Best practice
You should tune the cache refresh interval based on how frequently your application accesses data. If a multi-threaded
application or multiple amd-smi instances are only going to need information every 5 seconds, then set
the `AMD_GPU_METRICS_CACHE_MS` environment variable to something slightly less than 5 seconds.
```
AMD_GPU_METRICS_CACHE_MS = 4900 ms
```
In that way, the system is not constantly updating the cache from requests by each of the instances in the threads.