[ Note: cross-posted to linux-rt-users and oprofile-list ]
Hello,
The x86 Performance Monitoring Event "CPU_CLK_UNHALTED" is defined as:
Number of cycles during which the processor is not halted.
IIUC, when the CPU is in the HALT state, CPU_CLK_UNHALTED should not
increment, right? When Linux has nothing to do, it executes HLT.
http://lxr.linux.no/source/arch/i386/kernel/process.c#L101
I set up OProfile to sample EIP every 200000 CPU_CLK_UNHALTED cycles on
an idle system. I was expecting a very small number of samples, since
CPU_CLK_UNHALTED should not increment (most of the time).
I ran the daemon 5 minutes on a idle system
# opreport -l
CPU: PIII, speed 1266.7 MHz (estimated)
Counted CPU_CLK_UNHALTED events (clocks processor is not halted) with a
unit mask of 0x00 (No unit mask) count 200000
samples % symbol name
1868484 99.4914 cpu_idle
4560 0.2428 (oprofiled)
727 0.0387 ip_route_input
457 0.0243 acpi_ev_asynch_execute_gpe_method
454 0.0242 ip_route_output_slow
286 0.0152 dma_free_coherent
280 0.0149 ip_route_input_slow
273 0.0145 acpi_ex_opcode_6A_0T_1R
220 0.0117 __acpi_nmi_disable
130 0.0069 Dta1xxRxProcessStatusFlags
94 0.0050 Dta1xxTxProcessStatusFlags
93 0.0050 (bash)
85 0.0045 Dta1xxIsr
79 0.0042 intel_machine_check
56 0.0030 sys_olduname
51 0.0027 Dta1xxPeriodicIntHandler
cpu_idle breakdown:
c0100e70 1 5.4e-05
c0100e71 1 5.4e-05
c0100e78 1 5.4e-05
c0100e88 1 5.4e-05
c0100e8a 1 5.4e-05
c0100e97 4 2.1e-04
c0100ea8 1868475 99.9995
cpu_idle objdump:
c0100ea6: fb sti
c0100ea7: f4 hlt
c0100ea8: eb 0b jmp c0100eb5
(If an interrupt is used to resume execution after a HLT instruction,
the saved instruction pointer points to the instruction following the
HLT instruction.)
oprofiled collected 1878300 samples. In other words, the system received
1878300 NMIs. (5 * 60 * 1.2667e9) / 1878300 = 202316 cycles between NMI
Seems like CPU_CLK_UNHALTED increments every cycle.
Perhaps HLT does not put my CPU in the HALT state?
Did I miss something?
Regards.
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