Question & Answer
Question
Use this document to collect trace data for debugging high CPU usage related to cache lines usage.
Answer
This document applies only to IBM i on Power8
Cache line traces are a specific type of PEX trace. These traces can be used to help isolate which jobs, programs, and procedures are changing cache lines and contributing to CPU consumption. The trace is obtained using native OS/400 commands.
Cache line traces are a specific type of PEX trace. These traces can be used to help isolate which jobs, programs, and procedures are changing cache lines and contributing to CPU consumption. The trace is obtained using native OS/400 commands.
| 1. |
Confirm that the partition is running on Power8 hardware. The PEX definitions are specific to the hardware:
o DSPHDWRSC *PRC and press Enter. o Confirm that the listed Type-model, 9119-MME in the example below, is listed here: |
| 2. | Confirm that all required PEX PTFs are applied: http://public.dhe.ibm.com/services/us/igsc/idoctor/html/ptfs.html |
| 3. | Add the definition: ADDPEXDFN DFN(L3MISS) LEVEL(*SERVICE) TYPE(*TRACE) JOB((*ALL *ALL)) TASK(*ALL) MAXSTG(102400000) PMC(93 4 *TASK *NONE *NONE *NONE 0000014000016703) ITVSPEC(*COUNT) ITVCOUNT(1000) TRCTYPE(*SLTEVT) SLTEVT(*YES) BASEVT((*PMCO *NONE *FORMAT4)) TEXT('L3 Miss Format4 - Power8') |
| 4. |
Collect the data:
a. Issue the CRTLIB PEXDTA command, and press Enter.
b. Start the PEX trace: SBMJOB CMD(STRPEX SSNID(L3MISS) DFN(L3MISS)) JOBQ(QSYS/QSYSNOMAX) and press Enter. c. Run the workload. Gather for at least 10 minutes. This trace does not collect many events and can be run for as long as an hour. d. Stop the PEX trace: SBMJOB CMD(ENDPEX SSNID(L3MISS) DTALIB(PEXDTA)) JOBQ(QSYS/QSYSNOMAX) and press Enter. e. The submitted jobs must complete before moving to the next step. Note: If requested by IBM service, collect additional Optional Traces as described below. |
| 5. | Save the data and send it to IBM: a. CRTSAVF QGPL/PEXDTA and press Enter. b. SBMJOB CMD(SAVLIB LIB(PEXDTA) DEV(*SAVF) SAVF(QGPL/PEXDATA)) JOB(SAVLIB) JOBQ(QSYS/QSYSNOMAX) c. FTP the save file named PEXDTA in library QGPL to IBM: http://www-01.ibm.com/support/docview.wss?uid=nas8N1010370 |
| 6. | Clean-up: o DLTLIB PEXDTA and press Enter. |
Related Information
[{"Type":"MASTER","Line of Business":{"code":"LOB57","label":"Power"},"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SWG60","label":"IBM i"},"Platform":[{"code":"PF012","label":"IBM i"}],"Version":"7.1.0"}]
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Document Information
Modified date:
11 January 2022
UID
nas8N1021046