Lock Stall Analysis - 2025.2 English - UG1076

The Performance Metrics analysis tab can help identify if the lock stall needs to be analyzed. The following steps show how you can analyze a lock stall starting in the Vitis IDE:

1. Select the Trace view.
2. Select the Lock Stalls view.
   Tip: The Stalls view is available with the Trace view, Graph view, and Array view.
   Figure 1. Lock Stall in Trace View
   Each stall has the following information associated with it:

   NAME

   The name of the lock stall is LS_<NUM>. The number is unique across all types of stalls. The earlier the stall happens, the smaller the number.

   Stalled Tile

   The AI Engine tile that contains the stalled kernel.

   Stalled Kernel

   The stalled kernel. It is named <Kernel_function_name>.<Schedule_ID>.<Graph_instance_name>. If it displays as _main, you need to cross-probe to find the real kernel function.

   Start (ps)

   The start time of the stall.

   Duration (ps)

   The duration of the stall.

   PC

   Program counter when the stall happens.

   Type

   The stalled kernel tries to read or write the buffer.

   Buffer

   The buffer that the stalled kernel tries to read or write.

   Stalled Port

   The port of the stalled kernel that tries to read or write the buffer.

   Lock Holder

   The source that is holding the lock of the buffer.

   Related Stall

   Other stalls that can cause a stall.

   Tip: The items in green can be cross-probed with other views.

3. Select one row of the stall. It goes to the start of the stall in Trace view. You can optionally filter all the signals that relate to the stall by right-clicking the stall and choosing Filter Trace. The Trace view displays the signals that relate to the stall.
   Note: The Trace view hides unrelated signals. Exploring the trace is easier when the design is large.
   Tip: Filter Trace might not show signals related to the related stalls.
4. You can use Trace view to view the lock stall in a timeline. You can see it for a specific lock stall when the write lock and read lock are allocated. You can analyze the reason for the stall from the position of the stall and events before and after the stall.

   For example, write lock is already allocated and the lock type is Read. This indicates that the buffer has not been released by the producer. The consumer is waiting for it to be readable. The Lock Holder contains the producer.

5. To clear the previously filtered trace, right-click and choose Clear All Filters.
6. It is usually helpful to have an overview of the stall path in Graph view. Select Graph view and then select Tile View from the drop-down list in the view. Tile view of Graph view shows graph in AI Engine tiles.
7. If the Stalls view is not visible, select Lock Stalls from the drop-down list and choose the stall you want to analyze. The tool highlights the related paths in the Tile view of the Graph view.
8. The red path shows where the stall occurs. The white path shows the source to where the stall occurs.
9. Click the PC value. The source code opens and shows the line where the stall happens.