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# Improve load generator performance

This section includes recommendations for improving load generator performance. You can increase the number of file descriptors, process entries, and amount of swap space by configuring the kernel.

Note: Most operating systems using the Linux load generator have sufficient default file descriptors, process entries, and swap space, and rarely require reconfiguration.

In this topic:

## Increase file descriptors

A load generator uses the following file descriptor resources:

- 14 file descriptors for the launch service
- 20 file descriptors for the agent
- 30 file descriptors for each Vuser driver. By default, there is a driver for every 50 Vusers.
- File descriptors for the running Vusers. Each Vuser requires two descriptors.

For example, to compute the number of file descriptors used in running 100 threaded Vusers, the load generator requires:

Descriptors | Purpose of the descriptors
--- | ---
14 | For the launcher
20 | For the agent
60 | For 2 drivers (30 x 2, each one drives 50 Vusers)
200 | For 100 Vusers (each Vuser requires 2)

Total: 294 file descriptors

If Vusers are run as processes instead of threads, one driver is run per Vuser. Therefore, each Vuser requires 30 file descriptors.

The procedure to increase the number of file descriptors differs between shells.

In the examples below, the number of descriptors is increased to the maximum of 1024.

- For sh and ksh users, type:

      ulimit -n 1024

- For csh users, type:

      limit descriptors 1024

Below is an alternate procedure to increase file descriptors. In this example, the number of descriptors is increased to the maximum of 8192.

1. Add the following line to the /etc/security/limits.conf file:

       hard nfile 8192

2. Add the following line to the /etc/sysctl.conf file:

       fs.file-max = 8192

3. Reboot the machine.

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## Increase process entries

Each Vuser requires several free process entries. To increase the number of process entries on your system, you must reconfigure the kernel.

This section describes how to reconfigure the kernel for Linux platforms.

1. Locate the /etc/security/limits.conf file.

2. Set the maximum number of processes in the limits file. Type:

       hard nproc 8192

3. Reboot the machine.

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## Increase swap space

Each Vuser requires swap space ranging in size from 200 KB to 4 MB. Before adding space to your system configuration, you should determine your paging requirements. For environments running programs with very large memory requirements, it is recommended to have paging space of four times the physical memory. If you do not have enough paging space, certain processes may be killed, and others will be unable to start.

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See also:

- Install a load generator
- Prepare for installation

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