linux.git/arch/um/kernel/time.c, branch v7.0

um: Define timers on a per-CPU basis

2025-10-27T15:41:15+00:00

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: Indent time-travel help messages

2025-09-10T12:23:45+00:00

Indent the help messages for time-travel to make them consistent
with the format of other help messages.

Signed-off-by: Tiwei Bie 
Signed-off-by: Johannes Berg

um: Add missing trailing newline to help messages

2025-09-10T12:23:37+00:00

Some help messages are missing a trailing newline. They should
end with two newlines, but only one is present. Add the missing
newline to make the --help output more readable.

Signed-off-by: Tiwei Bie 
Signed-off-by: Johannes Berg

um: do not send SIGALRM to userspace in time-travel mode

2025-05-05T08:24:58+00:00

We send a SIGALRM to userspace processes to interrupt them. Really,
doing so is only needed if they are actually executing at the time (to
ensure we return to kernelspace). Unfortunately, we do not have that
information readily available. We can however be sure that this is never
the case when we are in time-travel mode with infinite CPU.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20250408074524.300153-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: insert scheduler ticks when userspace does not yield

2024-10-23T07:52:49+00:00

In time-travel mode userspace can do a lot of work without any time
passing. Unfortunately, this can result in OOM situations as the RCU
core code will never be run.

Work around this by keeping track of userspace processes that do not
yield for a lot of operations. When this happens, insert a jiffie into
the sched_clock clock to account time against the process and cause the
bookkeeping to run.

As sched_clock is used for tracing, it is useful to keep it in sync
between the different VMs. As such, try to remove added ticks again when
the actual clock ticks.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241010142537.1134685-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: Remove unused mm_fd field from mm_id

2024-09-12T18:36:22+00:00

It's no longer used since the removal of the SKAS3/4 support.

Signed-off-by: Tiwei Bie 
Signed-off-by: Richard Weinberger

um: time-travel: remove time_exit()

2024-07-03T15:09:08+00:00

This function is unused and unneeded, remove it.

Link: https://patch.msgid.link/20240703130105.02b3a974acb7.I7264821f7cfa17ea713b7a3e4787aa41a3107d01@changeid
Signed-off-by: Johannes Berg

um: add shared memory optimisation for time-travel=ext

2024-07-03T10:24:54+00:00

With external time travel, a LOT of message can end up
being exchanged on the socket, taking a significant
amount of time just to do that.

Add a new shared memory optimisation to that, where a
number of changes are made:
 - the controller sends a client ID and a shared memory FD
   (and a logging FD we don't use) in the ACK message to
   the initial START
 - the shared memory holds the current time and the
   free_until value, so that there's no need to exchange
   messages for that
 - if the client that's running has shared memory support,
   any client (the running one included) can request the
   next time it wants to run inside the shared memory,
   rather than sending a message, by also updating the
   free_until value
 - when shared memory is enabled, RUN/WAIT messages no
   longer have an ACK, further cutting down on messages

Together, this can reduce the number of messages very
significantly, and reduce overall test/simulation run time.

Co-developed-by: Mordechay Goodstein 
Signed-off-by: Mordechay Goodstein 
Link: https://patch.msgid.link/20240702192118.6ad0a083f574.Ie41206c8ce4507fe26b991937f47e86c24ca7a31@changeid
Signed-off-by: Johannes Berg

um: time-travel: support time-travel protocol broadcast messages

2024-07-03T10:24:22+00:00

Add a message type to the time-travel protocol to broadcast
a small (64-bit) value to all participants in a simulation.
The main use case is to have an identical message come to
all participants in a simulation, e.g. to separate out logs
for different tests running in a single simulation.

Down in the guts of time_travel_handle_message() we can't
use printk() and not even printk_deferred(), so just store
the message and print it at the start of the userspace()
function.

Unfortunately this means that other prints in the kernel
can actually bypass the message, but in most cases where
this is used, for example to separate test logs, userspace
will be involved. Also, even if we could use
printk_deferred(), we'd still need to flush it out in the
userspace() function since otherwise userspace messages
might cross it.

As a result, this is a reasonable compromise, there's no
need to have any core changes and it solves the main use
case we have for it.

Signed-off-by: Mordechay Goodstein 
Link: https://patch.msgid.link/20240702192118.c4093bc5b15e.I2ca8d006b67feeb866ac2017af7b741c9e06445a@changeid
Signed-off-by: Johannes Berg

um: time-travel: fix time-travel-start option

2024-07-03T10:21:16+00:00

We need to have the = as part of the option so that the
value can be parsed properly. Also document that it must
be given in nanoseconds, not seconds.

Fixes: 065038706f77 ("um: Support time travel mode")
Link: https://patch.msgid.link/20240417102744.14b9a9d4eba0.Ib22e9136513126b2099d932650f55f193120cd97@changeid
Signed-off-by: Johannes Berg