vasilito
6a5582783f
The proc scheme's Self::Priority write handler used 'kernel_prio = (20 - nice) as usize' which maps: nice -20 -> kernel_prio 40, clamped to 39 nice 0 -> kernel_prio 20 nice 19 -> kernel_prio 1 But SCHED_PRIO_TO_WEIGHT[39] = 15 (lowest weight, least CPU time), and SCHED_PRIO_TO_WEIGHT[0] = 88761 (highest weight, most CPU time). So the old formula gave processes that set nice to the most favorable value (-20) the LEAST CPU time, and processes that set nice to the least favorable value (+19) the MOST CPU time. Completely inverted. Correct formula: kernel_prio = (nice + 20) as usize, giving: nice -20 -> kernel_prio 0 (highest weight, most CPU) nice 0 -> kernel_prio 20 nice 19 -> kernel_prio 39 (lowest weight, least CPU) The corresponding read path (kernel_prio -> nice) is 'nice = (context.prio as i32 - 20)'. The old read was '(20 - context.prio as i32)' which had the same inversion plus a clamp that hid the bug for prio 0 (-> nice 20, clamped to 19, never returned the correct -20). Also fix the self-contradictory doc comment on Context:: set_sched_other_prio which claimed 'prio 39 is the lowest nice value (highest CPU weight)' — actually prio 0 is the highest weight and highest priority. Discovered by Oracle review of Phase 0c patches (Issue 29). The bug was introduced in the original P5-proc-setschedpolicy patch (before Phase 0c) and survived because the kernel boots with default priority 20 (nice 0), so the inversion was invisible during normal testing.
Kernel
Redox OS Microkernel
Requirements
nasmneeds to be available on the PATH at build time.
Building The Documentation
Use this command:
cargo doc --open --target x86_64-unknown-none
Debugging
QEMU
Running QEMU with the -s flag will set up QEMU to listen on port 1234 for a GDB client to connect to it. To debug the redox kernel run.
make qemu gdb=yes
This will start a virtual machine with and listen on port 1234 for a GDB or LLDB client.
GDB
If you are going to use GDB, run these commands to load debug symbols and connect to your running kernel:
(gdb) symbol-file build/kernel.sym
(gdb) target remote localhost:1234
LLDB
If you are going to use LLDB, run these commands to start debugging:
(lldb) target create -s build/kernel.sym build/kernel
(lldb) gdb-remote localhost:1234
After connecting to your kernel you can set some interesting breakpoints and continue
the process. See your debuggers man page for more information on useful commands to run.
Notes
-
Always use
foo.get(n)instead offoo[n]and try to cover for the possibility ofOption::None. Doing the regular way may work fine for applications, but never in the kernel. No possible panics should ever exist in kernel space, because then the whole OS would just stop working. -
If you receive a kernel panic in QEMU, use
pkill qemu-systemto kill the frozen QEMU process.
How To Contribute
To learn how to contribute to this system component you need to read the following document:
Development
To learn how to do development with this system component inside the Redox build system you need to read the Build System and Coding and Building pages.
How To Build
To build this system component you need to download the Redox build system, you can learn how to do it on the Building Redox page.
This is necessary because they only work with cross-compilation to a Redox virtual machine, but you can do some testing from Linux.
Funding - Unix-style Signals and Process Management
This project is funded through NGI Zero Core, a fund established by NLnet with financial support from the European Commission's Next Generation Internet program. Learn more at the NLnet project page.
