Linux has a set of events you can query to look at performance of … well lots of things. Its a generic mechanism. Here’s a quick peek at the set of values I can see if I look at an AltraMax running Fedora 36.

I’ve been looking in to PCIe+CXL. These are my notes.

ARM64 design defines features long before there is a CPU that can implement those features. Since the ARM ecosystem is so varied, there are many different CPU designs out there with different capabilities. A general purpose linux Kernel build put out by a major distribution has to work across a wide array of chips by a large nuymber of vendors. Thus, there is an enumeration of the capabilities inside the Kernel and mechnism for describing how to probe each of these capabilities.

We have reason to believe that we should not be setting CONFIG_EFI_DISABLE_RUNTIME=y In our Kernel configs. I want to perform a controlled expereient booting two Kernel builds, one with this option set and one with it disabled. Since I have the option set, building that Kernel is trivial.

 make olddefconfig
 make -j$(nproc)  rpm-pkg

Now, to turn that option off, I could just edit the .config file. However, it is possible that there are other config options linked to that one, and there is logic to modify them together. I want to see what happens if I use make menuconfig to change the option to confirm (or deny) that only that option gets changed. But where do I find this option in the menu?

I won’t go into checking out or building the Kernel, as that is covered elsewhere. Assuming you have a buildable Kernel, you can build the tests with:

make -C tools/testing/selftests

But you are probably going to see errors like this:

ksm_tests.c:7:10: fatal error: numa.h: No such file or directory
    7 | #include <numa.h>
      |          ^~~~~~~~
compilation terminated.

The userland test suites use several libraries and need headers to compile the tests that call those libraries. Here is the yum, line I ran to get the dependencies I needed for my system:

sudo yum install libmnl-devel fuse-devel numactl-devel libcap-ng-devel alsa-lib-devel

With those installed, the make line succeeded.

Running the test like this CRASHED THE SYSTEM. Don’t do this.

 make -C tools/testing/selftests run_tests

A more sensible test to run is the example on the Docs page:

# make -C tools/testing/selftests TARGETS=ptrace run_tests
make: Entering directory '/root/linux/tools/testing/selftests'
make --no-builtin-rules ARCH=arm64 -C ../../.. headers_install
make[1]: Entering directory '/root/linux'
  INSTALL ./usr/include
make[1]: Leaving directory '/root/linux'
make[1]: Entering directory '/root/linux/tools/testing/selftests/ptrace'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory '/root/linux/tools/testing/selftests/ptrace'
make[1]: Entering directory '/root/linux/tools/testing/selftests/ptrace'
TAP version 13
1..3
# selftests: ptrace: get_syscall_info
# TAP version 13
# 1..1
# # Starting 1 tests from 1 test cases.
# #  RUN           global.get_syscall_info ...
# #            OK  global.get_syscall_info
# ok 1 global.get_syscall_info
# # PASSED: 1 / 1 tests passed.
# # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
ok 1 selftests: ptrace: get_syscall_info
# selftests: ptrace: peeksiginfo
# PASS
ok 2 selftests: ptrace: peeksiginfo
# selftests: ptrace: vmaccess
# TAP version 13
# 1..2
# # Starting 2 tests from 1 test cases.
# #  RUN           global.vmaccess ...
# #            OK  global.vmaccess
# ok 1 global.vmaccess
# #  RUN           global.attach ...
 
 
# # attach: Test terminated by timeout
# #          FAIL  global.attach
# not ok 2 global.attach
# # FAILED: 1 / 2 tests passed.
# # Totals: pass:1 fail:1 xfail:0 xpass:0 skip:0 error:0
not ok 3 selftests: ptrace: vmaccess # exit=1
make[1]: Leaving directory '/root/linux/tools/testing/selftests/ptrace'
make: Leaving directory '/root/linux/tools/testing/selftests'

Next up is to write my own stub test.