[llvm-bugs] [Bug 39828] New: [llvm-mca] Add a 'memory' event type to track load/store queue usage.

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Nov 28 10:43:56 PST 2018


            Bug ID: 39828
           Summary: [llvm-mca] Add a 'memory' event type to track
                    load/store queue usage.
           Product: tools
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: llvm-mca
          Assignee: unassignedbugs at nondot.org
          Reporter: andrea.dibiagio at gmail.com
                CC: andrea.dibiagio at gmail.com, llvm-bugs at lists.llvm.org,
                    matthew.davis at sony.com

Once https://reviews.llvm.org/D54957 is committed, class SchedulerStatistics
will start correctly tracking the load/store queue consumption in the LSUnit.

However, SchedulerStatistics will work under the assumption that load/store
entries are reserved at 'instruction dispatched' stage, and released at
'instruction executed' stage. This currently matches the behavior of LSUnit.

That design will minimize the number of events generated by the
Dispatch/Execute stages, at the cost of doing extra bookkeeping in method
`onEvent()`. It also introduces a subtle (not-so-nice) dependency with how the
LSUnit works internally.

In future, we should add a new "memory queue" event type, so that
SchedulerStatistics will stop making assumptions on when/how queue entries are
allocated by the LSUnit.

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