add doc/PCM_IIO_README.md

Change-Id: Ib907de4f842848e9f0b63f398cfff2470ed9f55d

Author: rdementi

README.md

@@ -42,7 +42,7 @@ PCM provides a number of command-line utilities for real-time monitoring:
 
 - **pcm-latency** : monitor L1 cache miss and DDR/PMM memory latency
 - **pcm-pcie** : monitor PCIe bandwidth per-socket
-- **pcm-iio** : monitor PCIe bandwidth per PCIe device
+- **pcm-iio** : [monitor PCIe bandwidth per PCIe bus/device](doc/PCM_IIO_README.md)
 
 ![pcm-iio output](https://raw.githubusercontent.com/wiki/intel/pcm/pcm-iio.png)
 - **pcm-numa** : monitor local and remote memory accesses

doc/PCM_IIO_README.md

@@ -0,0 +1,31 @@
+## Purpose:
+
+PCM-IIO tool monitors PCIe transactions with a breakdown per PCIe bus (IIO stack) and/or PCIe devices.
+
+## Tool UI introduction:
+
+Inbound (PCIe device DMA into system) metrics:
+
+* IB write (inbound write): the number of bytes per second that the PCIe device requested to write to main memory through DMA
+* IB read (inbound read): the number of bytes per second that the PCIe device requested to read from main memory through DMA
+
+Outbound (CPU MMIO to the PCIe device):
+
+* OB read (outbound write): the number of bytes per second that the CPU requested to write to the PCIe device through MMIO (Memory-mapped I/O)
+* OB write (outbound read): the number of bytes per second that the CPU requested to read from the PCIe device through MMIO
+
+IOMMU metrics:
+
+* IOTLB Lookup: IOTLB lookups per second
+* IOTLB Miss: IOTLB misses per second
+* Ctxt Cache Hit: Context cache hits per second
+* 256T Cache Hit: Second Level Page Walk Cache Hits to a 256T page per second
+* 512G Cache Hit: Second Level Page Walk Cache Hits to a 512G page per second
+* 1G Cache Hit: Second Level Page Walk Cache Hits to a 1G page per second
+* 2M Cache Hit: Second Level Page Walk Cache Hits to a 2M page per second
+* IOMMU Mem Access: IOMMU memory accesses per second
+
+## Event config file:
+
+pcm-iio tool allows the user to customize the performance events with the config file as a an advanced feature. The event config files are opCode-x-y.txt where x/y is cpu family is model id, for example 6/143 for Sapphire Rapids.
+