xgboost/doc/gpu/index.md
Rory Mitchell 1b77903eeb
Fix several GPU bugs (#2916)
* Fix #2905

* Fix gpu_exact test failures

* Fix bug in GPU prediction where multiple calls to batch prediction can produce incorrect results

* Fix GPU documentation formatting
2017-12-04 08:27:49 +13:00

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XGBoost GPU Support
===================
This page contains information about GPU algorithms supported in XGBoost.
To install GPU support, checkout the [build and installation instructions](../build.md).
# CUDA Accelerated Tree Construction Algorithms
This plugin adds GPU accelerated tree construction and prediction algorithms to XGBoost.
## Usage
Specify the 'tree_method' parameter as one of the following algorithms.
### Algorithms
```eval_rst
+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tree_method | Description |
+==============+=======================================================================================================================================================================+
| gpu_exact | The standard XGBoost tree construction algorithm. Performs exact search for splits. Slower and uses considerably more memory than 'gpu_hist' |
+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| gpu_hist | Equivalent to the XGBoost fast histogram algorithm. Much faster and uses considerably less memory. NOTE: Will run very slowly on GPUs older than Pascal architecture. |
+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
```
### Supported parameters
```eval_rst
.. |tick| unicode:: U+2714
.. |cross| unicode:: U+2718
+----------------------+------------+-----------+
| parameter | gpu_exact | gpu_hist |
+======================+============+===========+
| subsample | |cross| | |tick| |
+----------------------+------------+-----------+
| colsample_bytree | |cross| | |tick| |
+----------------------+------------+-----------+
| colsample_bylevel | |cross| | |tick| |
+----------------------+------------+-----------+
| max_bin | |cross| | |tick| |
+----------------------+------------+-----------+
| gpu_id | |tick| | |tick| |
+----------------------+------------+-----------+
| n_gpus | |cross| | |tick| |
+----------------------+------------+-----------+
| predictor | |tick| | |tick| |
+----------------------+------------+-----------+
| grow_policy | |cross| | |tick| |
+----------------------+------------+-----------+
| monotone_constraints | |cross| | |tick| |
+----------------------+------------+-----------+
```
GPU accelerated prediction is enabled by default for the above mentioned 'tree_method' parameters but can be switched to CPU prediction by setting 'predictor':'cpu_predictor'. This could be useful if you want to conserve GPU memory. Likewise when using CPU algorithms, GPU accelerated prediction can be enabled by setting 'predictor':'gpu_predictor'.
The device ordinal can be selected using the 'gpu_id' parameter, which defaults to 0.
Multiple GPUs can be used with the grow_gpu_hist parameter using the n_gpus parameter. which defaults to 1. If this is set to -1 all available GPUs will be used. If gpu_id is specified as non-zero, the gpu device order is mod(gpu_id + i) % n_visible_devices for i=0 to n_gpus-1. As with GPU vs. CPU, multi-GPU will not always be faster than a single GPU due to PCI bus bandwidth that can limit performance.
This plugin currently works with the CLI, python and R - see installation guide for details.
Python example:
```python
param['gpu_id'] = 0
param['max_bin'] = 16
param['tree_method'] = 'gpu_hist'
```
## Benchmarks
To run benchmarks on synthetic data for binary classification:
```bash
$ python tests/benchmark/benchmark.py
```
Training time time on 1,000,000 rows x 50 columns with 500 boosting iterations and 0.25/0.75 test/train split on i7-6700K CPU @ 4.00GHz and Pascal Titan X.
```eval_rst
+--------------+----------+
| tree_method | Time (s) |
+==============+==========+
| gpu_hist | 13.87 |
+--------------+----------+
| hist | 63.55 |
+--------------+----------+
| gpu_exact | 161.08 |
+--------------+----------+
| exact | 1082.20 |
+--------------+----------+
```
[See here](http://dmlc.ml/2016/12/14/GPU-accelerated-xgboost.html) for additional performance benchmarks of the 'gpu_exact' tree_method.
## References
[Mitchell R, Frank E. (2017) Accelerating the XGBoost algorithm using GPU computing. PeerJ Computer Science 3:e127 https://doi.org/10.7717/peerj-cs.127](https://peerj.com/articles/cs-127/)
[Nvidia Parallel Forall: Gradient Boosting, Decision Trees and XGBoost with CUDA](https://devblogs.nvidia.com/parallelforall/gradient-boosting-decision-trees-xgboost-cuda/)
## Author
Rory Mitchell
Jonathan C. McKinney
Shankara Rao Thejaswi Nanditale
Vinay Deshpande
... and the rest of the H2O.ai and NVIDIA team.
Please report bugs to the xgboost/issues page.