I/O

These metrics show the performance of the I/O subsystem from the application’s point of view. Correlating these with the I/O time in the Application Activity chart helps to diagnose I/O bottlenecks.

POSIX I/O read rate

The total I/O read rate of the application. This might be greater than Disk read transfer if data is read from the cache instead of the storage layer.

POSIX I/O write rate

The total I/O write rate of the application. This may be greater than Disk write transfer if data is written to the cache instead of the storage layer.

Disk read transfer

The rate at which the application reads data from disk, in bytes per second. This includes data read from network filesystems (such as NFS), but might not include all local I/O due to page caching.

Disk write transfer

The rate at which the application writes data to disk, in bytes per second. This includes data written to network filesystems.

POSIX read syscall rate

The rate at which the application invokes the read system call. Measured in calls per second, not the amount of data transferred.

POSIX write syscall rate

The rate at which the application invokes the write system call. Measured in calls per second, not the amount of data transferred.

Note

  • Disk transfer and I/O metrics are not available on Cray X-series systems as the necessary Linux kernel support is not enabled.

  • I/O time in the Application Activity chart done using direct kernel calls is not counted.

  • Even if your application does not perform I/O, a non-zero amount of I/O is recorded at the start of profile because of internal I/O performed by Linaro MAP.