[Host-Trap PC Sampling] Host-Trap PC sampling an introduce an arbitrary sampling skid of [0, 2] instructions (#515)

* Arbitrary host-trap sampling skid (doc)

The host-trap PC sampling might introduce a skid of [0, 2]
instructions. We documented this information and provides
some advice to application developers how to find
hot-spots in the profiles generated by host-trap sampling.

source/docs/how-to/using-pc-sampling.rst

@@ -201,6 +201,31 @@ The preceding command generates a JSON file with the comprehensive output. Here
 
 For description of the fields in the JSON output, see :ref:`output-file-fields`.
 
+An Arbitrary Host-Trap PC Sampling Skid
+===============================================
+
+Host-Trap PC sampling is a software-based technique that utilizes a background kernel thread
+to periodically interrupt running waves in order to capture the program counter (PC).
+This method is effective for gathering performance data without requiring specialized hardware
+to snapshot the waves. However, it has limitations due to the potential delay between 
+when a wave receives an interrupt and when it processes the interrupt to capture the PC.
+This delay can lead to a sampling skid, where the PC samples may be attributed to instructions
+that are up to two instructions away from the actual source of latency.
+This results in a non-precise intra-kernel sampling method.
+
+When analyzing an application profile generated by host-trap PC sampling,
+developers should consider not only the reported most costly instruction but
+also the instructions immediately preceding or following it.
+If the costly instruction is near a branch instruction, it is important 
+to also consider the instruction targeted by the branch and the one immediately following it.
+
+To address the limitations of host-trap sampling, the hardware-based stochastic PC sampling method
+has been developed. This method provides precise intra-kernel sampling with zero sampling skid,
+offering more accurate performance insights.
+
+It is important to note that the skid issue inherent in host-trap PC sampling will not be resolved
+in its current form. Therefore, users are encouraged to adopt stochastic PC sampling,
+starting with the GFX942 architecture, to achieve more precise performance profiling.
 
 Hardware-Based (Stochastic) PC Sampling Method
 ===============================================
@@ -329,3 +354,4 @@ Fields starting with ``arb_state_`` are of particular interest as they indicate
 Namely, ``arb_state_issue_`` fields indicate what type of instructions arbiter issued at the time of sampling.
 On the other hand, ``arb_state_stall_`` fields indicate what type of instructions were stalled at the time of sampling.
 This information is useful for understanding how many instructions per cycle (IPC) are issued.
+