This was just RefPtr<OpenFileDescription> and descriptor flags.
Descriptor flags only define O_CLOEXEC, so we can just store fd's
cloexec status in a bitmap rather than separate fields. This cuts down
the size of OpenFileDescriptorSet to basically half!
Kernel syscall API no longer zeros all unused argument registers and
libc now uses inlined syscall macro internally. This significantly
cleans up generated code for basic syscall wrapper functions.
Instead of keeping track of the current time and rescheduling when
interval has passed, keep track of the next expected reschedule time.
This prevents theoretically missing every second pre-emption when
scheduler's timer is interrupting at same rate as the interval.
Initially allocate all physical memory except kernel memory and boot
modules. Before we just skipped all memory before kernel boot modules.
Also release memory used by boot modules after the kernel is up and
running. Once the boot modules are loaded, there is no need to keep them
in memory.
We now appreciate sa_mask and SA_NODEFER and change the signal mask for
the duration of signal handler. This is done by making a sigprocmask
syscall at the end of the signal handler. Back-to-back signals will
still grow stack as original registers are popped AFTER the block mask
is updated. I guess this is why linux has sigreturn(?).
Current cpu index is stored at either segment. If userspace sets that
segment, kernel will not overwrite it on every reschedule. This is fine
as long as user program does not use anything that relies on it :)
We need to have interrupts enabled when signal kills the process as
process does mutex locking. Also signals are now only checked when
returning to userspace in the same place where userspace segments are
loaded.
This removes unnecessary probing that lead to timeouts. Also cap codec
address at 14 instead of 15. My test laptop was duplicating codec 0 at
address 15 leading to duplicate devices.
Remove buffering from network layer and rework loopback interface.
loopback now has a separate recieve thread to allow concurrent sends and
prevent deadlocks
We now only send enough data to fill other ends window, not past that.
Previous logic had a but that allowed sending too much data leading to
retransmissions.
When the target sends zero window and later updates window size,
immediately retransmit non-acknowledged bytes.
Don't validate packets through listeing socket twice. The actual socket
will already verify the checksum so the listening socket does not have
to.
We now report actually available window size when sending packets. If
the available window size grows significantly we send an ACK to reflect
this to the remote.
Invalidations are not done if mapping or unmapping previously unmapped
page. TLB invalidate IPIs are now ignored if they don't affect the
currently mapped address space
Process's memory regions are now behind an rwlock instead of using the
full process lock. This allows most pointer validations to not block as
write operations to memory regions are rare.
Thread's userspace stack is now part of process's memory regions. This
simplifies code that explicitly looped over threads to see if the
accessed address was inside a thread's stack.
Only drawback of this is that MemoryRegions don't support guard pages,
so userspace stackoverflow will be handeled as cleanly as it was prior
to this.
This patch also fixes some unnecessary locking of the process lock and
moves locking to the internal helper functions instead of asserting that
the lock is held. Also we now make sure loaded ELF regions are in sorted
order as we previously expected.
Eeach futex object now has its own mutex to prevent unnecessary locking
of the process/global futex lock. This basically removes sys_futex from
profiles when running software with llvmpipe
There is no need to save and load sse state on every interrupt. Instead
we can use CR0.TS to make threads trigger an interrupt when they use sse
instructions. This can be used to only save and load sse state when
needed.
Processor now keeps track of its current "sse thread" and the scheduler
either enabled or disabled sse based on which thread it is starting up.
When a thread dies, it checks if it was the current sse thread to avoid
use after free bugs. When load balancing, processor has to save the
thread's sse state before sending it to a new processor (if it was the
current sse thread). This ensures thread's sse state will be correct
when the new processor ends up loading it.
Doing a yield no longer raises a software interrupt. Instead it just
saves all the callee saved registers, ip, sp and return value. Because
yield is only called in the kernel, it can just restore registers and
jump to the target address. There is never a need to use iret :)
If multiple threads were waiting for more block buffers without anyone
releasing them, they ended up in a deadlock.
Now we store 6 blocks for 8 threads. If a thread already has a block
buffer, it will not have to wait for a new one. Only if there are more
than 8 threads using blocks, will it block until there are free slots
for a thread available.
Add support for processor local futexes. These work the exact same way
as global ones, but only lock a process specific lock and use a process
specific hash map.
Also reduce the time futex lock is held. There was no need to hold the
global lock while validating addresses in the process' address space.
If the processor has invariant TSC it can be used to measure time. We
keep track of the last nanosecond and TSC values and offset them based
on the current TSC. This allows getting current time in userspace.
The implementation maps a single RO page to every processes' address
space. The page contains the TSC info which gets updated every 100 ms.
If the processor does not have invariant TSC, this page will not
indicate the capability for TSC based timing.
There was the problem about how does a processor know which cpu it is
running without doing syscall. TSC counters may or may not be
synchronized between cores, so we need a separate TSC info for each
processor. I ended up adding sequence of bytes 0..255 at the start of
the shared page. When a scheduler gets a new thread, it updates the
threads gs/fs segment to point to the byte corresponding to the current
cpu.
This TSC based timing is also used in kernel. With 64 bit HPET this
probably does not bring much of a benefit, but on PIT or 32 bit HPET
this removes the need to aquire a spinlock to get the current time.
This change does force the userspace to not use gs/fs themselves and
they are both now reserved. Other one is used for TLS (this can be
technically used if user does not call libc code) and the other for
the current processor index (cannot be used as kernel unconditionally
resets it after each load balance).
I was looking at how many times timer's current time was polled
(userspace and kernel combined). When idling in window manager, it was
around 8k times/s. When running doom it peaked at over 1 million times
per second when loading and settled at ~30k times/s.
