The sys$alarm() syscall has logic to cache a m_alarm_timer to avoid
allocating a new timer for every call to alarm. Unfortunately that
logic was broken, and there were conditions in which we could have
a timer allocated, but it was no longer on the timer queue, and we
would attempt to cancel that timer again resulting in an infinite
loop waiting for the timers callback to fire.
To fix this, we need to track if a timer is currently in use or not,
allowing us to avoid attempting to cancel inactive timers.
Luke and Tom did the initial investigation, I just happened to have
time to write a repro and attempt a fix, so I'm adding them as the
as co-authors of this commit.
Co-authored-by: Luke <luke.wilde@live.co.uk>
Co-authored-by: Tom <tomut@yahoo.com>
It's possible that a timer may have been queued to be executed by
the timer irq handler, but if we're in a critical section on the
same processor and are trying to cancel that timer, we would spin
forever waiting for it to be executed.
Note that there are a few minor differences between the InlineLinekdList
and IntrusiveList API, so this isn't just a pure data structure change.
- first()/last() instead of head()/tail()
- There is no need for a for_each(..) implementation, as it already
exposes the ability to do range based for loops.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
This commit is very invasive, because Thread likes to take a pointer and write
to it. This means that translating between timespec/timeval/Time would have been
more difficult than just changing everything that hands a raw pointer to Thread,
in bulk.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
This implements a number of changes related to time:
* If a HPET is present, it is now used only as a system timer, unless
the Local APIC timer is used (in which case the HPET timer will not
trigger any interrupts at all).
* If a HPET is present, the current time can now be as accurate as the
chip can be, independently from the system timer. We now query the
HPET main counter for the current time in CPU #0's system timer
interrupt, and use that as a base line. If a high precision time is
queried, that base line is used in combination with quering the HPET
timer directly, which should give a much more accurate time stamp at
the expense of more overhead. For faster time stamps, the more coarse
value based on the last interrupt will be returned. This also means
that any missed interrupts should not cause the time to drift.
* The default system interrupt rate is reduced to about 250 per second.
* Fix calculation of Thread CPU usage by using the amount of ticks they
used rather than the number of times a context switch happened.
* Implement CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE and use it
for most cases where precise timestamps are not needed.
This allows us to use blocking timeouts with either monotonic or
real time for all blockers. Which means that clock_nanosleep()
now also supports CLOCK_REALTIME.
Also, switch alarm() to use CLOCK_REALTIME as per specification.
We need to be able to guarantee that a timer won't be executing after
TimerQueue::cancel_timer returns. In the case of multiple processors
this means that we may need to wait while the timer handler finishes
execution on another core.
This also fixes a problem in Thread::block and Thread::wait_on where
theoretically the timer could execute after the function returned
and the Thread disappeared.
Use the TimerQueue to expire blocking operations, which is one less thing
the Scheduler needs to check on every iteration.
Also, add a BlockTimeout class that will automatically handle relative or
absolute timeouts as well as overriding timeouts (e.g. socket timeouts)
more consistently.
Also, rework the TimerQueue class to be able to fire events from
any processor, which requires Timer to be RefCounted. Also allow
creating id-less timers for use by blocking operations.
MemoryManager cannot use the Singleton class because
MemoryManager::initialize is called before the global constructors
are run. That caused the Singleton to be re-initialized, causing
it to create another MemoryManager instance.
Fixes#3226
The public consumers of the timer API shouldn't need to know
the how timer id's are tracked internally. Expose a typedef
instead to allow the internal implementation to be protected
from potential churn in the future.
It's also just good API design.
The current API of add_timer makes it hard to use as
you are forced to do a bunch of time arithmetic at the
caller. Ideally we would have overloads for common time
types like timespec or timeval to keep the API as straight
forward as possible. This change moves us in that direction.
While I'm here, we should really also use the machines actual
ticks per second, instead of the OPTIMAL_TICKS_PER_SECOND_RATE.
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).
As suggested by Joshua, this commit adds the 2-clause BSD license as a
comment block to the top of every source file.
For the first pass, I've just added myself for simplicity. I encourage
everyone to add themselves as copyright holders of any file they've
added or modified in some significant way. If I've added myself in
error somewhere, feel free to replace it with the appropriate copyright
holder instead.
Going forward, all new source files should include a license header.
PR #591 defines the rationale for kernel-level timers. They're most
immediately useful for TCP retransmission, but will most likely see use
in many other areas as well.
