DELL 2 x Intel Xeon E7-4860 338-BFMX User Manual

Datasheet Volume 2 of 2

47

Retries are the re-querying to other sockets to see if it this node can make transition to 
its desired package C-state. Retries are done when it is found that system state is 
changed which may cause previous responses from other sockets stale. The retry 
request is made in following scenario 

• When a node's (socket's) initial PMReq was not granted its desired package C-state 

but a higher power C-state.  In such case, socket's current package state is not 
same as its desired package state. If this socket receives an initial PMRreq from 
other nodes (initial request is an indication that some thing has change on system 
which might have changed the allowable lowest package C state on the system), it 
responds with its CmpD and send its PMReq retry for its own desired package 
C-state. 

• When a node receives an initial request from other nodes to a higher power C-state 

then its own desired package C-state, it needs to retry PMReq for its desire package 
C-state fresh co-ordination. 

• When a node has sent its PMReq request (initial or retry) and it receives an Initial 

PMReq from other node before it can get CmpD response for its request from all 
other populated nodes. It indicates that some of the some of the CmpD responses 
on the system can be stale. Once the node has received all the CmpD responses, it 
has to discard this response due to conflict and retry it's PMReq for fresh co-
ordination. 

Even through Ubox implements PMReq conflicts detection in hardware and provides this 
information to pcode but as per current implementation pcode ignores this information 
and does firmware conflict detection for simplicity and patch ability reasons. 

A receiving node has to respond to its inbound PMReq request by a CmpD response 
with the data in the response indicating the state_type it is willing other node to hold 
currently. In most case, through not all (for desired package C-state < C3 it responds 
with C0), a node provides its CmpD response which is same as its current desired 
package C-state.

The Outgoing PMReqs messages and the Inbound CmpD messages are new features on 
Intel Xeon Processor E7-8800/4800/2800 Product Families.

The PMReq interface handles four types of messages:

1. Outbound PMReq messages: 

a. Messages initiated by this node requesting permission from all other nodes for 

this node to transition to a "deeper" P/C/S/T state (Intel Xeon Processor E7-
8800/4800/2800 Product Families - will use only for C state), or

b. Messages initiated by this node to all other nodes announcing a transition of the 

node to a "shallower" P/C/S/T state (Intel Xeon Processor E7-8800/4800/2800 
Product Families - will use only for C state), or 

c. "Retry" messages initiated by this node in response to a new (not retried) PMReq 

message from another node when a previous request by this node was rejected.

2. Outbound CmpD messages: