Intel Xeon E5-2600 Series

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Reference Number: 327043-001 129

Intel® Xeon® Processor E5-2600 Product Family Uncore Performance Monitoring

VN0_CREDITS_USED

• Title: VN0 Credit Used

• Category: LINK_VN0_CREDITS Events

• Event Code: 0x36

• Max. Inc/Cyc: 1, Register Restrictions: 0-1

• Definition: Number of times a VN0 credit was used on the DRS message channel. In order for a

request to be transferred across Intel® QPI, it must be guaranteed to have a flit buffer on the

remote socket to sink into. There are two credit pools, VNA and VN0. VNA is a shared pool used to

achieve high performance. The VN0 pool has reserved entries for each message class and is used

to prevent deadlock. Requests first attempt to acquire a VNA credit, and then fall back to VN0 if

they fail. This counts the number of times a VN0 credit was used. Note that a single VN0 credit

holds access to potentially multiple flit buffers. For example, a transfer that uses VNA could use 9

flit buffers and in that case uses 9 credits. A transfer on VN0 will only count a single credit even

though it may use multiple buffers.

NDR bxxxxx1xx NDR Message Class:

NDR packets are used to transmit a variety of protocol flits including

grants and completions (CMP).

DRS bxxxx1xxx DRS Message Class:

Filter for Data Response (DRS). DRS is generally used to transmit

data with coherency. For example, remote reads and writes, or

cache to cache transfers will transmit their data using DRS.

NCB bxxx1xxxx NCB Message Class:

Filter for Non-Coherent Broadcast (NCB). NCB is generally used to

transmit data without coherency. For example, non-coherent read

data returns.

NCS bxx1xxxxx NCS Message Class:

Filter for Non-Coherent Standard (NCS). NCS is commonly used for

Table 2-140. Unit Masks for VN0_CREDITS_USED

Extension

umask

[15:8]

Description

HOM bxxxxxxx1 HOM Message Class:

Filter for the Home (HOM) message class. HOM is generally used to

send requests, request responses, and snoop responses.

SNP bxxxxxx1x SNP Message Class:

Filter for Snoop (SNP) message class. SNP is used for outgoing

snoops. Note that snoop responses flow on the HOM message class.