Divyansh Singhvi

Parallel I/O is an indispensable part of scientific applications. The current stack of parallel I/O contains many tunable parameters. While changing these parameters can increase I/O performance many-fold, the application developers usually resort to default values because tuning is a cumbersome process and requires expertise. We propose two auto-tuning models, based on active learning that recommend a good set of parameter values (currently tested with Lustre parameters and MPI-IO hints) for an application on a given system. These models use Bayesian optimization to find the values of parameters by minimizing an objective function. The first model runs the application to determine these values, whereas, the second model uses an I/O prediction model for the same. Thus the training time is significantly reduced in comparison to the first model (e.g., from 800 seconds to 18 seconds). Also both the models provide flexibility to focus on improvement of either read or write performance. To keep the tuning process generic, we have focused on both read and write performance. We have validated our models using an I/O benchmark (IOR) and 3 scientific application I/O kernels (S3D-IO, BT-IO and GenericIO) on two supercomputers (HPC2010 and Cori). Using the two models, we achieve an increase in I/O bandwidth of up to 11× over the default parameters. We got up to 3× improvements for 37 TB writes, corresponding to 1 billion particles in GenericIO. We also achieved up to 3.2× higher bandwidth for 4.8 TB of noncontiguous I/O in BT-IO benchmark.

Parallel I/O tuning is useful for scientific applications that read and write huge amounts of data. I/O performance depends on multiple tunable parameters such as the stripe size, stripe count, the collective I/O buffer size, and the number of collective I/O aggregators. The search space being large, it is cumbersome to tune the I/O parameters for every system to achieve optimal results. We propose active learning-based execution and prediction-based tuning models. These recommend a good set of I/O parameter values for an application on a given system. These models use optimization to find the parameter values; the objective is to minimize I/O time. The models allow to focus on improvement of read and/or write performance, and separate tuning of reads and writes. We evaluated our models using I/O kernels of scientific applications (S3D-IO, BT-IO and GenericIO) and the highly configurable IOR benchmark on an Intel-based supercomputer, HPC2010. We achieved an increase in I/O bandwidth of up to 8x over the default parameters, when both read and write are optimized together, and up to 20x in read bandwidths when optimized separately.