Before this change, we did a non-specific EOI, which could lead to
problems with other IRQs that are handled in the PIC. Since the original
8259A datasheet permits such functionality and we are not losing any
functionality, this change is acceptable even though we don't experience
problems with the EOI currently.
This is not a complete fix, since spurious IRQs under heavy loads can
still occur. However, this fix limits the amount of spurious IRQs.
It is encouraged to provide a better fix in the future, probably
something that takes into account handling of PCI level-triggered
interrupts.
Now we don't send raw numbers, but we let the IRQController object to
figure out the correct IRQ number.
This helps in a situation when we have 2 or more IOAPICs, so if IOAPIC
1 is assigned for IRQs 0-23 and IOAPIC 2 is assigned for IRQs 24-47,
if an IRQHandler of IRQ 25 invokes disable() for example, it will call
his responsible IRQController (IOAPIC 2), and the IRQController will
subtract the IRQ number with his assigned offset, and the result is that
the second redirection entry in IOAPIC 2 will be masked.
We don't return blindly the IRQ controller's model(), if the Spurious
IRQ handler is installed in IOAPIC environment, it's misleading to
return "IOAPIC" string since IOAPIC doesn't really handle Spurious
IRQs, therefore we return a "" string.
FlyString is a flyweight string class that wraps a RefPtr<StringImpl>
known to be unique among the set of FlyStrings. The class is very
unoptimized at the moment.
When to use FlyString:
- When you want O(1) string comparison
- When you want to deduplicate a lot of identical strings
When not to use FlyString:
- For strings that don't need either of the above features
- For strings that are likely to be unique
This new subsystem includes better abstractions of how time will be
handled in the OS. We take advantage of the existing RTC timer to aid
in keeping time synchronized. This is standing in contrast to how we
handled time-keeping in the kernel, where the PIT was responsible for
that function in addition to update the scheduler about ticks.
With that new advantage, we can easily change the ticking dynamically
and still keep the time synchronized.
In the process context, we no longer use a fixed declaration of
TICKS_PER_SECOND, but we call the TimeManagement singleton class to
provide us the right value. This allows us to use dynamic ticking in
the future, a feature known as tickless kernel.
The scheduler no longer does by himself the calculation of real time
(Unix time), and just calls the TimeManagment singleton class to provide
the value.
Also, we can use 2 new boot arguments:
- the "time" boot argument accpets either the value "modern", or
"legacy". If "modern" is specified, the time management subsystem will
try to setup HPET. Otherwise, for "legacy" value, the time subsystem
will revert to use the PIT & RTC, leaving HPET disabled.
If this boot argument is not specified, the default pattern is to try
to setup HPET.
- the "hpet" boot argumet accepts either the value "periodic" or
"nonperiodic". If "periodic" is specified, the HPET will scan for
periodic timers, and will assert if none are found. If only one is
found, that timer will be assigned for the time-keeping task. If more
than one is found, both time-keeping task & scheduler-ticking task
will be assigned to periodic timers.
If this boot argument is not specified, the default pattern is to try
to scan for HPET periodic timers. This boot argument has no effect if
HPET is disabled.
In hardware context, PIT & RealTimeClock classes are merely inheriting
from the HardwareTimer class, and they allow to use the old i8254 (PIT)
and RTC devices, managing them via IO ports. By default, the RTC will be
programmed to a frequency of 1024Hz. The PIT will be programmed to a
frequency close to 1000Hz.
About HPET, depending if we need to scan for periodic timers or not,
we try to set a frequency close to 1000Hz for the time-keeping timer
and scheduler-ticking timer. Also, if possible, we try to enable the
Legacy replacement feature of the HPET. This feature if exists,
instructs the chipset to disconnect both i8254 (PIT) and RTC.
This behavior is observable on QEMU, and was verified against the source
code:
ce967e2f33
The HPETComparator class is inheriting from HardwareTimer class, and is
responsible for an individual HPET comparator, which is essentially a
timer. Therefore, it needs to call the singleton HPET class to perform
HPET-related operations.
The new abstraction of Hardware timers brings an opportunity of more new
features in the foreseeable future. For example, we can change the
callback function of each hardware timer, thus it makes it possible to
swap missions between hardware timers, or to allow to use a hardware
timer for other temporary missions (e.g. calibrating the LAPIC timer,
measuring the CPU frequency, etc).
A new IP address or a new network mask can be specified in the command
line arguments of ifconfig to replace the old values of a given network
adapter. Additionally, more information is being printed for each adapter.
This is similar to 28e1da344d
and 4dd4dd2f3c.
The crux is that wait verifies that the outvalue (siginfo* infop)
is writable *before* waiting, and writes to it *after* waiting.
In the meantime, a concurrent thread can make the output region
unwritable, e.g. by deallocating it.
This is similar to 28e1da344d
and 4dd4dd2f3c.
The crux is that select verifies that the filedescriptor sets
are writable *before* blocking, and writes to them *after* blocking.
In the meantime, a concurrent thread can make the output buffer
unwritable, e.g. by deallocating it.
