diff options
| -rw-r--r-- | faq/smp.mdwn | 6 | ||||
| -rw-r--r-- | hurd/running/debian/qemu_image.mdwn | 2 | ||||
| -rw-r--r-- | open_issues/smp.mdwn | 248 |
3 files changed, 5 insertions, 251 deletions
diff --git a/faq/smp.mdwn b/faq/smp.mdwn index ee0bf53f..c8b20da8 100644 --- a/faq/smp.mdwn +++ b/faq/smp.mdwn @@ -21,12 +21,12 @@ This needs testing as SMP support has recently been added to Mach. Intel_iPSC/860]], so principally has the required infrastructure. It has recently been enhanced to support nowadays' SMP standards like ACPI. -However, [[GNU Mach|microkernel/mach/gnumach]]'s Linux device driver glue -code isn't SMP-safe so build with --disable-linux-groups to test SMP and use +However, [[GNU Mach|microkernel/mach/gnumach]]'s Linux device driver glue code +isn't SMP-safe so the in-kernel drivers will be disabled, and one has to use rumpdisk to provide disk access. To build an SMP supported gnumach with kdb: -../configure --enable-ncpus=8 --enable-kdb --enable-apic --disable-linux-groups +../configure --enable-ncpus=8 --enable-kdb This will by default allow you to boot with one core isolated to the default processor set, and all the other detected cpus will be in the slave processor set. diff --git a/hurd/running/debian/qemu_image.mdwn b/hurd/running/debian/qemu_image.mdwn index bd299579..c6da1555 100644 --- a/hurd/running/debian/qemu_image.mdwn +++ b/hurd/running/debian/qemu_image.mdwn @@ -42,7 +42,7 @@ Optionally you may use `--curses` to keep your keyboard layout. If need be modpr Note that if you do not have a command named `kvm`, you can try something across the lines of: - $ qemu-system-i386 --enable-kvm -M q35 -m 2G -drive cache=writeback,file=$(echo debian-hurd-*.img) -net user,hostfwd=tcp:127.0.0.1:2222-:22 -net nic,model=e1000 + $ qemu-system-i386 --enable-kvm -m 2G -drive cache=writeback,file=$(echo debian-hurd-*.img) -net user,hostfwd=tcp:127.0.0.1:2222-:22 -net nic,model=e1000 Or, if your machine does not allow for KVM acceleration, omit `--enable-kvm` from the command. diff --git a/open_issues/smp.mdwn b/open_issues/smp.mdwn index 9820f561..ce2c2ce2 100644 --- a/open_issues/smp.mdwn +++ b/open_issues/smp.mdwn @@ -56,7 +56,7 @@ Once you have the Hurd running you can build an SMP enabled GNU Mach. $ autoreconf -i $ mkdir build $ cd build - $ ../configure --enable-ncpus=4 --enable-apic --enable-kdb --disable-linux-groups + $ ../configure --enable-ncpus=4 --enable-kdb $ make gnumach.gz $ su # mv /boot/gnumach-1.8-486.gz /boot/gnumach-1.8-486.gz.bak @@ -88,252 +88,6 @@ To test smp: smp.c source can be found [[here|https://lists.gnu.org/archive/html/bug-hurd/2024-02/msg00088.html]]. -# What was done to get the 32-bit SMP support - -The GNU Mach source code includes many special cases for multiprocessor, -controlled by #if NCPUS > 1 macro. - -But this support is very limited: - -- GNU Mach don't detect CPUs in runtime: The number of CPUs must be hardcoded in -compilation time. The number of cpus is set in `mach_ncpus` configuration -variable, set to 1 by default, in configfrag.ac file. This variable will -generate `NCPUS` macro, which is used by gnumach to control the special cases -for multiprocessor. If `NCPUS` > 1, then gnumach will enable multiprocessor -support, with the number of cpus set by the user in mach_ncpus -variable. Otherwise, SMP will be disabled. - -- The special cases to multicore in gnumach source code have never been tested, - so these can contain many errors. Furthermore, these special case are - incomplete: many functions, such as `cpu_number()` or `intel_startCPU()` aren't - written. - -- GNU Mach doesn't initialize the processor with the proper options for - multiprocessing. For this reason, the current support is only multithread and - not real multiprocessor support. - -- Many drivers included in Hurd aren't thread-safe, and these could crash in a - SMP environment. So, it's necessary to isolate this drivers, to avoid - concurrency problems. - - -### Solution - -To solve this, we need to implement some routines to detect the number of -processors, assign an identifier to each processor, and configure the lapic and -IPI support. These routines must be executed during Mach boot. - -> "Really, all the support you want to get from the hardware is just getting the -> number of processors, initializing them, and support for interprocessor -> interrupts (IPI) for signaling." - Samuel Thibault -> [link](https://lists.gnu.org/archive/html/bug-hurd/2018-08/msg00071.html) - -> "The process scheduler probably already has the support. What is missing is -the hardware driver for SMP: enumeration and initialization." - Samuel Thibault -[link](https://lists.gnu.org/archive/html/bug-hurd/2018-08/msg00083.html) - -The current necessary functions are `cpu_number()` (in kern/cpu_number.h) and -`intel_startCPU()`. Another non-critical function, is `cpu_control()` -[*Reference*](https://www.gnu.org/software/hurd/gnumach-doc/Processor-Control.html#Processor-Control) - -Other interesting files are `pmap.c` and `sched_prim.c` We also -have to build an isolated environment to execute the non-thread-safe drivers. - -> "Yes, this is a real concern. For the Linux drivers, the long-term goal is to -> move them to userland anyway. For Mach drivers, quite often they are not -> performance-sensitive, so big locks would be enough." - Samuel Thibault -> [link](https://lists.gnu.org/archive/html/bug-hurd/2018-08/msg00073.html) - -### Task list - -1. DONE Implement a routine to detect and identify the processors - - This routine must check the number of processors, initialize the lapic of BSP - (the master processor), and assign a kernel ID for each processor. This kernel - ID does not have to be equal to the APIC ID. The relation kernel/APIC can be - settled with an array, where the kernel ID is the index, and the APIC contains - the data. GNU Mach can derive the list of processors from memory, reading from - ACPI table, or from MP table. However, MP table is deprecated in most modern - CPUs, so it is preferable to use ACPI table for this. - - The tasks to do for this are: - - - Detect the number of processors - - - Create a array indexed by kernel ID, which sets a relation with APIC ID. - - - Initialize the lapic of BSP - - - Initialize IOAPIC - - This routine could be called from `i386at_init()` - (i386/i386at/model_dep.c). This function will call the functions which - initialize the lapic and the ioapic. - - **NOTE**: This routine must be executed before `intel_startCPU()` or other routines. - - - **How to find APIC table** - - To find APIC table, we can read - RSDT table [RSDT reference](http://www.uefi.org/sites/default/files/resources/ACPI%206_2_A_Sept29.pdf#G10.1358180). - To get the address of RSDT, we need to read RDSP table. We can get the - RSDP table by this [RDSP - reference](http://www.uefi.org/sites/default/files/resources/ACPI%206_2_A_Sept29.pdf#G10.1357698) - Once we have the RSDT table, we need to read *Entry* field, and search the pointer to - the APIC table in the array referenced in this field. - - We can find an example about reading ACPI table in X15 OS: - [Reference](https://github.com/richardbraun/x15/blob/0c0e2a02a42a8161e1b8dc1e1943fe5057ecb3a3/arch/x86/machine/acpi.c#L576) - - - We need to initialize the `machine_slot` of each processor (currently only initializes cpu0). - The `machine_slot` has this structure. [Reference](https://github.com/AlmuHS/GNUMach_SMP/blob/0d490ef21c156907f3f26a6cdc00842f462a877a/include/mach/machine.h#L68): - - > `struct machine_slot { /*boolean_t*/` <br/> - > `integer_t is_cpu;` <br/> - > `/* is there a cpu in this slot? */ ` <br/> - > `cpu_type_t cpu_type; /* type of cpu */` <br/> - > `cpu_subtype_t cpu_subtype; /* subtype of cpu */` <br/> - > `/*boolean_t*/ integer_t running; /* is cpu running */` <br/> - > `integer_t cpu_ticks[CPU_STATE_MAX]; integer_t` <br/> - > `clock_freq; /* clock interrupt frequency */ };` <br/> - - - We can find an example of initialization in this [link:](https://github.com/AlmuHS/GNUMach_SMP/blob/0d490ef21c156907f3f26a6cdc00842f462a877a/i386/i386at/model_dep.c#L612) - - This modification also involve the redefinition of `NCPUS`, which must be set - to the maximum **possible** number of processors. We can do this by modifying - `configfrag.ac`, with this: - - > `# Multiprocessor support is still broken.` <br/> - > `AH_TEMPLATE([MULTIPROCESSOR], [set things up for a uniprocessor])` <br/> - > `mach_ncpus=2` <br/> - > `AC_DEFINE_UNQUOTED([NCPUS], [$mach_ncpus], [number of CPUs])` </br> - > `[if [$mach_ncpus` > `-gt 1 ]; then]` <br/> - > `AC_DEFINE([MULTIPROCESSOR], [1], [set things up for a` > `multiprocessor])` - > `AC_DEFINE_UNQUOTED([NCPUS], [256], [number of CPUs]) ` <br/> - > `[fi]` <br/> - - - Interesting files and functions - `machine.c` - [Link](https://github.com/AlmuHS/GNUMach_SMP/blob/master/kern/machine.c) - - `c_boot_entry()` - [Link](https://github.com/AlmuHS/GNUMach_SMP/blob/0d490ef21c156907f3f26a6cdc00842f462a877a/i386/i386at/model_dep.c#L529) - - - Example, in X15 OS: - [Link](https://github.com/richardbraun/x15/blob/d6d90a3276a09da65690b019e985392bf77b53b0/arch/x86/machine/cpu.c#L1114) - - 1.1. Implement a `cpu_number()` function. - - - This function must return the kernel ID of the processor which is executing the function. To - get this, we have to read the local apic memory space, which will show the - lapic of the current CPU. Reading the lapic, we can get its APIC ID. Once - we have the APIC ID of the current CPU, the function will search in the - Kernel/APIC array until it finds the same APIC ID. Then it will return the - index (Kernel ID) of this position. - -2. DONE Implement a routine to initialize the processors - - - This routine will initialize the lapic of each processor and other structures - needed to run the kernel. We can find an example of lapic initialization - here - [reference](https://github.com/mit-pdos/xv6-public/blob/b818915f793cd20c5d1e24f668534a9d690f3cc8/lapic.c#L55) - Also, we can get more information in Chapter 8.4 and 8.11 of Intel - Developer Guide, - Volume 3. [link](https://software.intel.com/sites/default/files/managed/a4/60/325384-sdm-vol-3abcd.pdf) - -3. DONE Implement `intel_startCPU()` - - - This function will initialize the descriptor tables of the processor specified by the - parameter, and launch the startup IPI to this processor. This function will be - executed during the boot of the kernel (process 0). The task to do in this function - are: - - - Initialize the processor descriptor tables - - Launch Startup IPI to this processor - We have a current implementation of `intel_startCPU()` in this - [link](https://github.com/AlmuHS/GNUMach_SMP/blob/smp/i386/i386/mp_desc.c). - This implementation is based in XNU's `intel_startCPU()` - [function](https://github.com/nneonneo/osx-10.9-opensource/blob/f5a0b24e4d98574462c8f5e5dfcf0d37ef7e0764/xnu-2422.1.72/osfmk/i386/mp.c#L423) - - We can find explainations about how to raise an IPI in this pages: - [*Reference 1*](https://www.cs.usfca.edu/~cruse/cs630f08/lesson22.ppt), - [*Reference 2*](https://www.cheesecake.org/sac/smp.html), [*Reference - 3*](http://www.dis.uniroma1.it/pub/quaglia/AOSV-traps-interrupts.pdf) We can - get information about how to raise an IPI in Intel Developer Guide, Volume 3, - Chapter 10.6 - -4. Implement another routine to start the processors - - - This routine calls to `processor_start()` for each processor, which will start the - processor using this sequence of calls: [`processor_start(processor_t - processor)`](https://github.com/AlmuHS/GNUMach_SMP/blob/5d527f532dfba9f2da54555d5fbe585dd458579b/kern/processor.c#L447) - -> - [`cpu_start(processor->slot_num)`](https://github.com/AlmuHS/GNUMach_SMP/blob/5d527f532dfba9f2da54555d5fbe585dd458579b/i386/i386/mp_desc.c#L335) - -> - [`intel_startCPU(cpu)`](https://github.com/AlmuHS/GNUMach_SMP/blob/5d527f532dfba9f2da54555d5fbe585dd458579b/i386/i386/mp_desc.c#L180) - - These articles shows some annotations about how to do the AP Startup: - - - [Reference1](https://wiki.osdev.org/Symmetric_Multiprocessing#AP_startup), - - [Reference2](https://stackoverflow.com/a/16368043/7077301) (...) - - After implement IPI support, It's recommended reimplement `machine_idle()`, - `machine_relax ()`, `halt_cpu()` and `halt_all_cpus()` using IPI. - - [reference](https://github.com/AlmuHS/GNUMach_SMP/blob/0d490ef21c156907f3f26a6cdc00842f462a877a/i386/i386at/model_dep.c#L201) - - Also in `ast_check.c`, we have to implement both functions, using - IPI - [Reference](https://github.com/AlmuHS/GNUMach_SMP/blob/master/i386/i386/ast_check.c) - - - This functions must force the processors to check if there are any AST - signal, and we ought to keep in the mind the following irc chat: - - -> <AlmuHS> what is the use of AST in gnumach? <br/> -> <AlmuHS> this file what do? <br/> -> https://github.com/AlmuHS/GNUMach_SMP/blob/master/i386/i386/ast_check.c <br/> -> <youpi> I don't know <br/> -> <youpi> but look at what calls that <br/> -> <youpi> see e.g. the call in thread.c <br/> -> <AlmuHS> This <br/> -> function is called during the sequence of cpu_up(), in machine.c <br/> -> <AlmuHS> but only if NCPUS > 1 <br/> -> <youpi> it seems like it's to trigger an AST check on another <br/> -> processor <br/> -> <youpi> i.e. a processor tells another to run ast_check <br/> -> <youpi> (see the comment in thread.c) <br/> -> <AlmuHS> <br/> -> https://github.com/AlmuHS/GNUMach_SMP/blob/master/kern/machine.c <br/> -> <youpi> well, the initialization part is not necessarily what's -> important to <br/> -> think about at first <br/> -> <youpi> i.e. until you know what you'll have <br/> -> to do during execution, you don't know what you'll need to intialize at <br/> -> initialization <br/> -> <youpi> you might even not need to initialize anything <br/> -> <AlmuHS> then, this is the reason because all functions <br/> -> in ast_check.c are empty <br/> -> <youpi> cause_ast_check being empty is really probably a TODO <br/> -> <AlmuHS> but I'm not clear what I need to write in this functions <br/> -> <youpi> what the comment said: make another processor run ast_check() <br/> -> <youpi> which probably means raising an inter-processor interrupt <br/> -> <youpi> (aka IPI) <br/> -> <youpi> to get ast_check() called by the other processor <br/> -> <AlmuHS> then, this funcions must raise an IPI in the processor? <br/> -> <youpi> that's the idea <br/> -> <youpi> the IPI probably needs some setup <br/> - -We can use [XV6 source - code](https://pdos.csail.mit.edu/6.828/2018/xv6.html). as model to implements - the function and routines. Some interesting files are - [`lapic.c`](https://github.com/mit-pdos/xv6-public/blob/master/lapic.c), - [`proc.c`](https://github.com/mit-pdos/xv6-public/blob/master/proc.c) and - [`main.c`](https://github.com/mit-pdos/xv6-public/blob/master/main.c) - - ## References - [Comments about the project bug-hurd maillist](https://lists.gnu.org/archive/html/bug-hurd/2018-08/msg00048.html) |