6.5.2 Bottleneck analysis at SBSX and HN-I bridges

The CCN-502 provides events that observe the locations where the nodes or bridges are full, which can cause delays in the rest of the system. This enables you to monitor the current bottlenecks in the system, and checks multiple events in all CCN-502 components.

The events monitor the following:

  • The number of times the bridge is forced to retry because of the lack of dynamic credits.

  • The number of requests that have the ReqOrder information set. This event is only applicable in the HN-I.

The following events are used to measure bottlenecks at the SBSX and HN-I bridges:

Request retry rate at SBSX and HN-I bridges

Request retries from the SBSX are tracked in the HN-F.

Retry requests from the HN-I are tracked in the RN-I.

ReqOrder request rate

When requests are received at the HN-I with the ReqOrder bit set, they must maintain order, and are serialized. This event can be used to indicate a lower than expected bandwidth on the HN-I.

TXREQ_REQORDERNumber of requests that the HN-I observes with the ReqOrder bit set. This event is a measure of oversubscription in the read request tracker.

Calculate the ReqOrder request rate as follows:

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This event is tracked in the DWM, not in the SBSX or HN-I design.
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