kernel/arch/um/os-Linux/time.c, branch linux-rolling-stable

um: Add initial SMP support

2025-10-27T15:41:15Z

Add initial symmetric multi-processing (SMP) support to UML. With this support enabled, users can tell UML to start multiple virtual processors, each represented as a separate host thread. In UML, kthreads and normal threads (when running in kernel mode) can be scheduled and executed simultaneously on different virtual processors. However, the userspace code of normal threads still runs within their respective single-threaded stubs. That is, SMP support is currently available both within the kernel and across different processes, but still remains limited within threads of the same process in userspace. Signed-off-by: Tiwei Bie Link: https://patch.msgid.link/20251027001815.1666872-6-tiwei.bie@linux.dev Signed-off-by: Johannes Berg

um: Define timers on a per-CPU basis

2025-10-27T15:41:15Z

Define timers on a per-CPU basis to enable each CPU to have its own timer. This is a preparation for adding SMP support. Signed-off-by: Tiwei Bie Link: https://patch.msgid.link/20251027001815.1666872-5-tiwei.bie@linux.dev Signed-off-by: Johannes Berg

um: Determine sleep based on need_resched()

2025-10-27T15:41:15Z

With SMP and NO_HZ enabled, the CPU may still need to sleep even if the timer is disarmed. Switch to deciding whether to sleep based on pending resched. Additionally, because disabling IRQs does not block SIGALRM, it is also necessary to check for any pending timer alarms. This is a preparation for adding SMP support. Signed-off-by: Tiwei Bie Link: https://patch.msgid.link/20251027001815.1666872-4-tiwei.bie@linux.dev Signed-off-by: Johannes Berg

um: Remove unused timeval_to_ns() function

2022-03-11T09:49:50Z

The timeval_to_ns() function doesn't appear to be used anywhere, as far as I (or git grep) can tell, and clang throws up a warning about it: ../arch/um/os-Linux/time.c:21:25: warning: unused function 'timeval_to_ns' [-Wunused-function] static inline long long timeval_to_ns(const struct timeval *tv) ^ 1 warning generated. Signed-off-by: David Gow Acked-By: Anton Ivanov Signed-off-by: Richard Weinberger

um: fix os_idle_sleep() to not hang

2021-01-26T21:11:38Z

Changing os_idle_sleep() to use pause() (I accidentally described it as an empty select() in the commit log because I had changed it from that to pause() in a later revision) exposed a race condition in the idle code. The following can happen: timer_settime(0, 0, {it_interval={tv_sec=0, tv_nsec=0}, it_value={tv_sec=0, tv_nsec=624017}}, NULL) = 0 ... pause() and we now hang forever. This was previously possible as well, but it could never cause UML to hang for more than a second since we could only sleep for that much, so at most you'd notice a "hiccup" in the UML. Obviously, any sort of external interrupt also "saves" it and interrupts pause(). Fix this by properly handling the race, rather than papering over it again: - first, block SIGALRM, and obtain the old signal set - check the timer - suspend, waiting for any signal out of the old set, if, and only if, the timer will fire in the future - restore the old signal mask This ensures race-free operation: as it's blocked, the signal won't be delivered while we're looking at the timer even if it were to be triggered right _after_ we've returned from timer_gettime() with a non-zero value (telling us the timer will trigger). Thus, despite getting to sigsuspend() because timer_gettime() told us we're still waiting, we'll not hang because sigsuspend() will return immediately due to the pending signal. Fixes: 49da38a3ef33 ("um: Simplify os_idle_sleep() and sleep longer") Signed-off-by: Johannes Berg Acked-By: Anton Ivanov Signed-off-by: Richard Weinberger

um: Simplify os_idle_sleep() and sleep longer

2020-12-13T21:22:37Z

There really is no reason to pass the amount of time we should sleep, especially since it's just hard-coded to one second. Additionally, one second isn't really all that long, and as we are expecting to be woken up by a signal, we can sleep longer and avoid doing some work every second, so replace the current clock_nanosleep() with just an empty select() that can _only_ be woken up by a signal. We can also remove the deliver_alarm() since we don't need to do that when we got e.g. SIGIO that woke us up, and if we got SIGALRM the signal handler will actually (have) run, so it's just unnecessary extra work. Similarly, in time-travel mode, just program the wakeup event from idle to be S64_MAX, which is basically the most you could ever simulate to. Of course, you should already have an event in the list that's earlier and will cause a wakeup, normally that's the regular timer interrupt, though in suspend it may (later) also be an RTC event. Since actually getting to this point would be a bug and you can't ever get out again, panic() on it in the time control code. Signed-off-by: Johannes Berg Acked-By: Anton Ivanov Signed-off-by: Richard Weinberger

um: Move timer-internal.h to non-shared

2020-03-29T21:28:43Z

This file isn't really shared, it's only used on the kernel side, not on the user side. Remove the include from the user-side and move the file to a better place. While at it, rename it to time-internal.h, it's not really just timers but all kinds of things related to timekeeping. Signed-off-by: Johannes Berg Signed-off-by: Richard Weinberger

um: Add SPDX headers for files in arch/um/os-Linux

2019-09-15T19:37:17Z

Convert files to use SPDX header. All files are licensed under the GPLv2. Signed-off-by: Alex Dewar Signed-off-by: Richard Weinberger

um: Pass nsecs to os timer functions

2019-07-02T21:27:29Z

This makes the code clearer and lets the time travel patch have the actual time used for these functions in just one place. Signed-off-by: Johannes Berg Signed-off-by: Richard Weinberger

um: Timer code cleanup

2019-07-02T21:27:00Z

There are some unused functions, and some others that have unused arguments; clean up the timer code a bit. Signed-off-by: Johannes Berg Signed-off-by: Richard Weinberger