Front End Bandwidth Limited Due To Supply Out Of The Legacy Decode Pipeline

Front End Bandwidth Limited Due To Supply Out Of The Legacy Decode Pipeline

Charlie Hewett (Intel)'s picture

TITLE: Front End Bandwidth Limited Due To Supply Out Of The Legacy Decode Pipeline

ISSUE_NAME: Frontend^FE_bandwidth^MITE

DESCRIPTION:

Cycles the front end was bound on bandwidth supply out of MITE, which is the legacy decode pipeline

RELEVANCE:

When the front end cannot deliver enough uops when the back end is requesting uops, this can potentially indicate a front end limitation which is affecting performance.  With this metric, the limited bandwidth is due to limitations in the legacy decode pipeline being unable to supply 4 uops in a particular cycle.  Recommendation is to look into the other legacy decode pipeline related metrics to root cause the issue.

EXAMPLE:

Excessive resteers (from instructions which are decoded into two to four micro-ops) would be an example of how the front end bandwith may be limited in the legacy decode pipeline.

SOLUTION:

RELATED_SOURCES:

NOTES:

EQUATION:  (IDQ.ALL_MITE_CYCLES_ANY_UOPS-IDQ.ALL_MITE_CYCLES_4_UOPS) / CPU_CLK_UNHALTED.THREAD

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