- kernel maintains a cpu_info array which contains various
information about each cpu as filled when each cpu boots
- the information contains idetification, features etc.
- sometimes the system needs to know precisely on what type of cpu is
running. The cpu type id detected during arch specific
initialization and kept in the machine structure for later use.
- as a side-effect the information is exported to userland
- when a process is migrated to a different CPU it may have an active
FPU context in the processor registers. We must save it and migrate
it together with the process.
- pressing 'B' on the serial cnsole prints statistics for BKL per cpu.
- 'b' resets the counters
- it presents number of cycles each CPU spends in kernel, how many
cycyles it spends spinning while waiting for the BKL
- it shows optimistic estimation in how many cases we get the lock
immediately without spinning. As the test is not atomic the lock may
be already held by some other cpu before we actually try to acquire
it.
- each CPU has its own runqueues
- processes on BSP are put on the runqueues later after a switch to
the final stack when cpuid works to avoid special cases
- enqueue() and dequeue() use the run queues of the cpu the process is
assigned to
- pick_proc() uses the local run queues
- printing of per-CPU run queues ('2') on serial console
- kernel detects CPUs by searching ACPI tables for local apic nodes
- each CPU has its own TSS that points to its own stack. All cpus boot
on the same boot stack (in sequence) but switch to its private stack
as soon as they can.
- final booting code in main() placed in bsp_finish_booting() which is
executed only after the BSP switches to its final stack
- apic functions to send startup interrupts
- assembler functions to handle CPU features not needed for single cpu
mode like memory barries, HT detection etc.
- new files kernel/smp.[ch], kernel/arch/i386/arch_smp.c and
kernel/arch/i386/include/arch_smp.h
- 16-bit trampoline code for the APs. It is executed by each AP after
receiving startup IPIs it brings up the CPUs to 32bit mode and let
them spin in an infinite loop so they don't do any damage.
- implementation of kernel spinlock
- CONFIG_SMP and CONFIG_MAX_CPUS set by the build system
- most global variables carry information which is specific to the
local CPU and each CPU must have its own copy
- cpu local variable must be declared in cpulocal.h between
DECLARE_CPULOCAL_START and DECLARE_CPULOCAL_END markers using
DECLARE_CPULOCAL macro
- to access the cpu local data the provided macros must be used
get_cpu_var(cpu, name)
get_cpu_var_ptr(cpu, name)
get_cpulocal_var(name)
get_cpulocal_var_ptr(name)
- using this macros makes future changes in the implementation
possible
- switching to ELF will make the declaration of cpu local data much
simpler, e.g.
CPULOCAL int blah;
anywhere in the kernel source code
- kernel turns on IO APICs if no_apic is _not_ set or is equal 0
- pci driver must use the acpi driver to setup IRQ routing otherwise
the system cannot work correctly except systems like KVM that use
only legacy (E)ISA IRQs 0-15
- the ability for kernel to use ACPI tables to detect IO APICs. It is
the bare minimum the kernel needs to know about ACPI tables.
- it will be used to find out about processors as the MPS tables are
deprecated by ACPI and not all vendorsprovide them.
- FPU context is stored only if conflict between 2 FPU users or while
exporting context of a process to userspace while it is the active
user of FPU
- FPU has its owner (fpu_owner) which points to the process whose
state is currently loaded in FPU
- the FPU exception is only turned on when scheduling a process which
is not the owner of FPU
- FPU state is restored for the process that generated the FPU
exception. This process runs immediately without letting scheduler
to pick a new process to resolve the FPU conflict asap, to minimize
the FPU thrashing and FPU exception hadler execution
- faster all non-FPU-exception kernel entries as FPU state is not
checked nor saved
- removed MF_USED_FPU flag, only MF_FPU_INITIALIZED remains to signal
that a process has used FPU in the past
There seems to have been a broken assumption in the fpu context
restoring code. It restores the context of the running process, without
guarantee that the current process is the one that will be scheduled.
This caused fpu saving for a different process to be triggered without
fpu hardware being enabled, causing an fpu exception in the kernel. This
practically only shows up with DEBUG_RACE on. Fix my thruby+me.
The fix
. is to only set the fpu-in-use-by-this-process flag in the
exception handler, and then take care of fpu restoring when
actually returning to userspace
And the patch
. translates fpu saving and restoring to c in arch_system.c,
getting rid of a juicy chunk of assembly
. makes osfxsr_feature private to arch_system.c
. removes most of the arch dependent code from do_sigsend
ask to map in oxpcie i/o memory and support serial i/o for it in the
kernel. set oxpcie=<address> in boot monitor (retrieve address using
pci_debug=1 output). (no sanity checking is done on the address
currently.) disabled by default.
The change also contains some other minor cleanup (a new serial.h to set
register info common to UART and the OXPCIe card, in-kernel memory
mapping a little more structured and env_get() to get sysenv variables
without knowing about the params_buffer).
- this patch only renames schedcheck() to switch_to_user(),
cycles_accounting_stop() to context_stop() and restart() to
+restore_user_context()
- the motivation is that since the introduction of schedcheck() it has
been abused for many things. It deserves a better name. It should
express the fact that from the moment we call the function we are in
the process of switching to user.
- cycles_accounting_stop() was originally a single purpose function.
As this function is called at were convenient places it is used in
for other things too, e.g. (un)locking the kernel. Thus it deserves
a better name too.
- using the old name, restart() does not call schedcheck(), however
calls to restart are replaced by calls to schedcheck()
[switch_to_user] and it calls restart() [restore_user_context]
- this patch moves the former printslot() from arch_system.c to
debug.c and reimplements it slightly. The output is not changed,
however, the process information is printed in a separate function
print_proc() in debug.c as such a function is also handy in other
situations and should be publicly available when debugging.
this patch does not add or change any functionality of do_ipc(), it
only makes things a little cleaner (hopefully).
Until now do_ipc() was responsible for handling all ipc calls. The
catch is that SENDA is fairly different which results in some ugly
code like this typecasting and variables naming which does not make
much sense for SENDA and makes the code hard to read.
result = mini_senda(caller_ptr, (asynmsg_t *)m_ptr, (size_t)src_dst_e);
As it is called directly from assembly, the new do_ipc() takes as
input values of 3 registers in reg_t variables (it used to be 4,
however, bit_map wasn't used so I removed it), does the checks common
to all ipc calls and call the appropriate handler either for
do_sync_ipc() (all except SENDA) or mini_senda() (for SENDA) while
typecasting the reg_t values correctly. As a result, handling SENDA
differences in do_sync_ipc() is no more needed. Also the code that
uses msg_size variable is improved a little bit.
arch_do_syscall() is simplified too.
