Question & Answer
Question
Use this document to collect PEX trace data for debugging high CPU usage related to cache lines usage.
Answer
This document applies only to IBM i on Power10 and Power11
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 Power10 or Power11 hardware. The PEX definitions are specific to the hardware: o DSPHDWRSC *PRC and press Enter. o Confirm that the Type-model is listed here: https://www.ibm.com/docs/en/power10 or https://www.ibm.com/docs/en/power11 |
| 2. | Confirm that all required PEX PTFs are applied: http://public.dhe.ibm.com/services/us/igsc/idoctor/html/ptfs.html |
| 3. | Add the PEX definition: ADDPEXDFN DFN(L3MISS) LEVEL(*SERVICE) TYPE(*TRACE) JOB((*ALL *ALL)) TASK(*ALL) MAXSTG(102400000) PMC(165 3 *TASK *NONE *NONE *NONE *NONE) ITVSPEC(*COUNT) ITVCOUNT(1000) TRCTYPE(*SLTEVT) SLTEVT(*YES) BASEVT((*PMCO *NONE *FORMAT4)) TEXT('PM_MRK_DATA_FROM_L3MISS *FORMAT4 - P10') |
| 4. | Collect the PEX 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: https://www.ibm.com/support/pages/qmgtools-ftp-data-ibm |
| 6. | Clean-up: o DLTLIB PEXDTA and press Enter. |
Related Information
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Document Information
Modified date:
05 August 2025
UID
ibm16603427