Sampling Buffer Size

The VTune(TM) Performance Analyzer stores the samples (32 bytes per sample) collected during the Activity run in the sampling buffer. When the buffer is full, the VTune analyzer suspends sampling, writes the data to the disk and then resumes sampling. Sampling data is not collected while the data is being written to the disk.

Considerations for Defining the Buffer Size

• The sampling buffer is reserved and not available to other processes during the collection.

• The maximum sampling buffer size should be much less than the physical RAM on a machine. For example, on a machine with 256MB RAM, specify a fraction of 256MB, such as 8MB, as the sampling buffer size.

• The smaller the sampling buffer size, the more frequently the sampling collector suspends sampling in order to flush the buffer and write the data to the disk. Consider increasing the sampling buffer size if you want to reduce the number of times the sampling collector suspends sampling.

• The larger the buffer size, the longer the sampling collector takes to flush the buffer and write the data to the disk.

• If the buffer size is larger than what the sampling collector can allocate, the sampling collector fails.

To adjust the sampling buffer size:

1. From the Configure Sampling dialog box, select the General tab.

2. Enter the buffer size in the Sampling buffer size field.

To adjust the sampling buffer size from the command line:

use -sb | -sample-buffer-size <size in kilobytes>.

Command-line example:

>vtl activity -c sampling -o "-sb 2222"

Note

The default sampling buffer size is 2000KB.