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The MSR_PEBS_DATA_CFG MSR register is used to configure which data groups should be generated into a PEBS record, and it's shared among all counters. If there are different configurations among counters, perf combines all the configurations. The first perf command as below requires a complete PEBS record (including memory info, GPRs, XMMs, and LBRs). The second perf command only requires a basic group. However, after the second perf command is running, the MSR_PEBS_DATA_CFG register is cleared. Only a basic group is generated in a PEBS record, which is wrong. The required information for the first perf command is missed. $ perf record --intr-regs=AX,SP,XMM0 -a -C 8 -b -W -d -c 100000003 -o /dev/null -e cpu/event=0xd0,umask=0x81/upp & $ sleep 5 $ perf record --per-thread -c 1 -e cycles:pp --no-timestamp --no-tid taskset -c 8 ./noploop 1000 The first PEBS event is a system-wide PEBS event. The second PEBS event is a per-thread event. When the thread is scheduled out, the intel_pmu_pebs_del() function is invoked to update the PEBS state. Since the system-wide event is still available, the cpuc->n_pebs is 1. The cpuc->pebs_data_cfg is cleared. The data configuration for the system-wide PEBS event is lost. The (cpuc->n_pebs == 1) check was introduced in commit: |
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| .. | ||
| amd | ||
| intel | ||
| zhaoxin | ||
| core.c | ||
| Kconfig | ||
| Makefile | ||
| msr.c | ||
| perf_event_flags.h | ||
| perf_event.h | ||
| probe.c | ||
| probe.h | ||
| rapl.c | ||
| utils.c | ||