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== VTune Tutorial 3: Disk input Output Analysis ==
This is the workflow of I/O Analysis
[[File:O_analysis_work_flow.png|400px]]
Image Reference: https://software.intel.com/en-us/node/680296
== What is Disk I/O analysis ==
Disk input / output analysis is a platform-wide analysis that monitors the utilization of the disk subsystem, CPU and processor buses.
It requires the program to be run as administrator.
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What it is used for is to identify the imbalances between I/O operations and computational operations, as well as times the latency of the I/O requests.
As shown in the model there is multiple types of analysis.
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Analyze I/O data in System Cache mode
Command Line Arguments: -f out.txt -m c
In this mode, the application asynchronously writes records (16 Byte) to the output file, relying on system file cache.
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Analyze I/O data in System Cache and buffer mode
Command Line Arguments: -f out.txt -m b
Used to minimized the CPU usage and effectively use the I/O device. It combines the usage of system file cache and user buffer
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Analyze I/O data in Synchronous user and buffer mode
Command Line Argument: -f out.txt -m s
Used in the user buffer to further optimize the operation, program is I/O bound
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Analyze I/O data in Asynchronous user and buffer mode
Command Line Argument: -f out.txt -m a
Uses two user buffers and asynchronously submits data to the disk
== Running the I/O Analysis ==
The being the Disk Input/Output data analysis
We must first click on the new analysis button as show in the screenshot below:
[[File:Button.JPG|400px]]
We then proceed to input analysis target tab which would take us here
[[File:Menu display.JPG|400px]]
Make sure the check box for inherit settings from visual studio project is unchecked as shown:
[[File:Unchecked.JPG|400px]]
We then enter in the parameters for system cache mode and then proceed by clicking choose analysis
[[File:Click.JPG|400px]]
Upon getting to the page click the Disk Input and Output to start the analysis
[[File:Menu display 2.JPG|400px]]
The result page should pop up and it should show the summary page
[[File:Result 1.JPG|400px]]
On this page there is useful information to know whether the program is running efficiently, by opening the CPU time it shows a more detailed timings of how effective the program ran.
By looking at these times we can see the I/O wait times within the program. A more in-depth view of this is inside the Platform tab
[[File:Result 2.JPG|400px]]
In this page we can see where the I/O wait times are within which threads, so we can optimize it.
To view more in-depth results we would perform a new analysis with the next commands following the work flow model.
== Resources ==