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7. Advanced Workload controls

In the ADVANCED workload mode, MEXTEX starts up a number of independant scheduled threads, each of which generate and feed I/O requests to a number of I/O execution threads, i.e. each scheduler can have a number of simultaneous outstanding I/O requests. The number of scheduler threads is selectable by the user thru manipulation of the GUI, however the number of I/O execution threads is determined indirectly by the maximum number of processes which can be sproc'ed on the host machine.

The scheduler threads generate I/O requests based on the settings of a rich set of user manipulable controls. The user can construct a wide range of synthetic workloads by appropriate settings of the controls which determine

1. Percentage of reads vs. writes.
2. Percentage of Sequential I/Os vs. random I/Os.
3. Distribution of I/O request lengths.
4. Distribution of block address (LBA) locality.
5. Distribution of inter-I/O times.
6. Activity duty-cycle and period.

The following controls are available for determining the stream of I/Os generated.

* Number of I/O threads
Determines the number of independant scheduler threads created per device.
* Maximum number of queued I/Os
Determines the maximum number of queued I/Os per device.
* % Read I/Os
Determines the % of I/Os which will involve a read.
* % Read I/Os
Determines the % of I/Os which will involve a write.
* % Sequential I/Os
Determines the % of I/Os which will be sequential; that is, the start block address (LBA) of the I/O will be sequential with respect to the previous I/O.
* % Random I/Os
Determines the % of I/Os which will be random; that is, the start block address (LBA) of the I/O will be independent of the previous I/O.
* Sequential I/O Length Distribution
Determines the distribution of I/O request length for sequential I/Os.
* Random I/O Length Distribution
Determines the distribution of I/O request length for random I/Os.
* I/O alignment boundary
Determines the LBA boundaries of I/O requests. e.g. if the I/O alignment boundary is set to 4, LBAs of all requests will be multiples of 4.
* I/O Starting Distribution
Determines the distribution of I/O request starting block address (LBA) of random I/Os.
* Inter I/O time distribution
Determines the distribution of inter-I/O times.
* Activity Period
Defines the activity period needed by the Activity Duty Cycle control below.
* Activity Duty Cycle
Determines the activity/idle duty cycle; that is, the percentage of time that the device being exercised is kept busy vs. the percentage of time that the device is idle.

7.1. GUI Distribution controls

Distribution controls are used in a number of instances in the Advanced Workload controls. They provide a mechanism for controlling random number generators. Four controls are available; minimum and maximum values, a mode (one of UNIFORM, GAUSSIAN or POISSON) and a parameter value (SD when mode is GAUSSIAN, or MU when mode is POISSON).
* UNIFORM
When the distribution mode is UNIFORM, an integral random number is selected with uniform probability from the range determined by the minimum and maximum values.
* GAUSSIAN
When the distribution mode is GAUSSIAN, an integral random number is selected with normal (gaussian) probability from the range determined by the minimum and maximum values. The mean of the gaussian distribution is determined by the average of the minimum and maximum values, and the standard deviation is determined by the value of SD.
* POISSON
When the distribution mode is POISSON, an integral random number is selected with poisson probability from the range determined by the minimum and maximum values. The mean of the poisson distribution is determined by the value of MU.

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