- time stops if there is no activity and the timer expired before
we halted the cpu
- restart_local_timer() checks if the timer has expired and if so it
restarts it
- we do the same when switching back to userspace
- skip processes that are not asynsending to the target
- do not clear whole asynsend table upon IPC permission error
- be more accepting when one table entry is bogus later on
completed (successfully or not). AMF_NOTIFY_ERR can be used if the sender
only wishes to be notified in case of an error (e.g., EDEADSRCDST). A new
endpoint ASYNCM will be the sender of the notification.
- flush TLB of processes only if the page tables has been changed and
the page tables of this process are already loaded on this cpu which
means that there might be stale entries in TLB. Until now SMP was
always flushing TLB to make sure everything is consistent.
- accidentaly this wasn't part of the SMP merge and the implementation
remained uncomplete with the timer keeping ticking periodically
- APIC timer is set for a signel shot and restarted everytime it
expires. This way we can keep the AP's trully idle
- the timer is restarted a little later before leaving to userspace
- LAPIC_TIMER_ICR is written before LAPIC_LVTTR so the newest value is
used
- the Intel architecture cycle counter (performance counter) does not
count when the CPU is idle therefore we use busy loop instead of
halting the cpu when there is nothing to schedule
- the downside is that handling interrupts may be accounted as idle
time if a sample is taken before we get out of the nested trap and
pick a new process
- contributed by Bjorn Swift
- adds process accounting, for example counting the number of messages
sent, how often the process was preemted and how much time it spent
in the run queue. These statistics, along with the current cpu load,
are sent back to the user-space scheduler in the Out Of Quantum
message.
- the user-space scheduler may choose to make use of these statistics
when making scheduling decisions. For isntance the cpu load becomes
especially useful when scheduling on multiple cores.
- 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.
- this makes sure that each process always run with updated TLB
- this is the simplest way how to achieve the consistency. As it means
significant performace degradation when not require, this is nto the
final solution and will be refined
- APIC timer always reprogrammed if expired
- timer tick never happens when in kernel => never immediate return
from userspace to kernel because of a buffered interrupt
- renamed argument to lapic_set_timer_one_shot()
- removed arch_ prefix from timer functions
- any cpu can use smp_schedule() to tell another cpu to reschedule
- if an AP is idle, it turns off timer as there is nothing to
preempt, no need to wakeup just to go back to sleep again
- if a cpu makes a process runnable on an idle cpu, it must wake it up
to reschedule
- 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
- for better readability xpp is substitued by sender
- makes sure that the dequeued sender has p_q_link == NULL and that
this condition holds when enqueuing the sender again. This is a
sanity check to make sure that the new sender is not enqueued
already
- Before this change the dequeued sender's p_q_link may not be NULL
and it was only set to NULL when enqueued again
- removes p_delivermsg_lin item from the process structure and code
related to it
- as the send part, the receive does not need to use the
PHYS_COPY_CATCH() and umap_local() couple.
- The address space of the target process is installed before
delivermsg() is called.
- unlike the linear address, the virtual address does not change when
paging is turned on nor after fork().
- 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
- removes dependency of do_safecopy() on the m_type field of the kcall
messages.
- instead of do_safecopy() figuring out what action is requested, the
correct safecopy method is called right away.
- Currently the cpu time quantum is timer-ticks based. Thus the
remaining quantum is decreased only if the processes is interrupted
by a timer tick. As processes block a lot this typically does not
happen for normal user processes. Also the quantum depends on the
frequency of the timer.
- This change makes the quantum miliseconds based. Internally the
miliseconds are translated into cpu cycles. Everytime userspace
execution is interrupted by kernel the cycles just consumed by the
current process are deducted from the remaining quantum.
- It makes the quantum system timer frequency independent.
- The boot processes quantum is loosely derived from the tick-based
quantas and 60Hz timer and subject to future change
- the 64bit arithmetics is a little ugly, will be changes once we have
compiler support for 64bit integers (soon)
- 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]
it does this by
- making all processes interruptible by running out of quantum
- giving all processes a single tick of quantum
- picking a random runnable process instead of in order, and
from a single pool of runnable processes (no priorities)
This together with very high HZ values currently provokes some race conditions
seen earlier only when running with SMP.
