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play a bit with the ARM PMU

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Ciro Santilli 六四事件 法轮功
2020-11-18 00:00:00 +00:00
parent 95430c7c0c
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7 changed files with 142 additions and 22 deletions
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@@ -10206,6 +10206,7 @@ TODO exercise DMA on the kernel module. The `edu` hardware model has that featur
* https://stackoverflow.com/questions/32592734/are-there-any-dma-driver-example-pcie-and-fpga/44716747#44716747
* https://stackoverflow.com/questions/62831327/add-memory-device-to-qemu
* https://stackoverflow.com/questions/64539528/qemu-pci-dma-read-and-pci-dma-write-does-not-work
* https://stackoverflow.com/questions/64842929/general-protection-error-while-tring-to-perform-ioctl
===== Manipulate PCI registers directly
@@ -21881,6 +21882,16 @@ and:
Due to the way that <<gem5-syscall-emulation-multithreading>> however, the output is more deterministic in that case, see that section for further details.
[[perf-event-open]]
==== `perf_event_open` system call
link:userland/linux/perf_event_open.c[] counts instructions of a given loop: https://stackoverflow.com/questions/13313510/quick-way-to-count-number-of-instructions-executed-in-a-c-program/64863392#64863392
Bibliography:
* `man perf_event_open`
* https://community.arm.com/developer/ip-products/system/b/embedded-blog/posts/using-the-arm-performance-monitor-unit-pmu-linux-driver
=== Linux calling conventions
A summary of results is shown at: xref:table-linux-calling-conventions[xrefstyle=full].
@@ -22758,15 +22769,10 @@ produces:
There is also the RDPID instruction that reads just the processor ID, but it appears to be very new for QEMU 4.0.0 or <<p51>>, as it fails with SIGILL on both.
Bibliography: https://stackoverflow.com/questions/22310028/is-there-an-x86-instruction-to-tell-which-core-the-instruction-is-being-run-on/56622112#56622112
Bibliography:
===== ARM PMCCNTR register
TODO We didn't manage to find a working ARM analogue to <<x86-rdtsc-instruction>>: link:kernel_modules/pmccntr.c[] is oopsing, and even it if weren't, it likely won't give the cycle count since boot since it needs to be activate before it starts counting anything:
* https://stackoverflow.com/questions/40454157/is-there-an-equivalent-instruction-to-rdtsc-in-arm
* https://stackoverflow.com/questions/31620375/arm-cortex-a7-returning-pmccntr-0-in-kernel-mode-and-illegal-instruction-in-u/31649809#31649809
* https://blog.regehr.org/archives/794
* ARM has an analogous <<arm-pmccntr-register>>
* https://stackoverflow.com/questions/22310028/is-there-an-x86-instruction-to-tell-which-core-the-instruction-is-being-run-on/56622112#56622112
=== x86 thread synchronization primitives
@@ -23965,6 +23971,24 @@ Bibliography:
* <<arm-lse>>
=== ARM PMU
The PMU (Performance Monitor Unit) is an unit in the ARM CPU that counts performance events of interest. These can be used to benchmark, and sometimes debug, code running on ARM CPUs.
The <<linux-kernel>> exposes some (all?) of those events through the arch-agnostic <<perf-event-open>> system call.
The PMU is exposed through <<arm-system-register-instructions>>, with registers that start with the prefix `PM*`.
Bibliography: https://community.arm.com/developer/ip-products/system/b/embedded-blog/posts/using-the-arm-performance-monitor-unit-pmu-linux-driver
==== ARM PMCCNTR register
TODO We didn't manage to find a working ARM analogue to <<x86-rdtsc-instruction>>: link:kernel_modules/pmccntr.c[] is oopsing, and even it if weren't, it likely won't give the cycle count since boot since it needs to be activate before it starts counting anything:
* https://stackoverflow.com/questions/40454157/is-there-an-equivalent-instruction-to-rdtsc-in-arm
* https://stackoverflow.com/questions/31620375/arm-cortex-a7-returning-pmccntr-0-in-kernel-mode-and-illegal-instruction-in-u/31649809#31649809
* https://blog.regehr.org/archives/794
=== ARM assembly bibliography
==== ARM non-official bibliography
@@ -28171,6 +28195,12 @@ Those files also contain arch specific helpers under ifdefs like:
We try to keep as much as possible in those files. It bloats builds a little, but just makes everything simpler to understand.
Link with lkmc.o is enabled with the <<path-properties>>
....
'extra_objs_lkmc_common': False,
....
[[lkmc-home]]
==== lkmc_home