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Visual Studio Team System

How to: Collect Line-Level Sampling Data

Line-level sampling is the ability of the profiler to determine where in the code of a processor intensive function, such as a function with high exclusive samples, the processor has to spend most of its time.

For line-level sampling, the profiler walks the program call stack at regular intervals and aggregates those results. These results show what instructions the processor was executing when the samples were taken. The collected data about exclusive samples is then analyzed to identify the lines of code and the instruction pointer (IP).

Line-level sampling works for managed as well as native code. Performance reports that display this data include the Lines view and the Modules view.

Character begin/end information is not available for native code. For multi-line statements, line begin information is not available for native code; only line end information is available.

Available Data

Available line-level sampling data includes the following information:

  • Function name.

  • Function address.

  • Line begin –line number of the sampled code.

  • Line end – ending source line number. This is generally the same as the "Line begin" data except when a single program statement spans multiple source code lines.

  • Character begin – beginning column of the aggregate sample. This is generally 0 except when a single line contains multiple program statements.

  • Character end – ending column of the aggregate sample.

  • IP –address where the aggregate sample was taken (IP view only).

In Modules view, if a function has line-level statistics, the statistics are nested under each function. Additionally, IP-level statistics that are nested under each line are presented.

Turn Off Line-level Sampling for Managed Code

By default, line-level sampling is turned on. You can turn off line-level data collection for managed code by doing one of the following:

  • Before profiling, type VSPerfCLREnv /samplelineoff. This affects both applications and services.

    — or —

  • When starting an application, type VSPerfCmd /lineoff <other arguments>.