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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 <mordechay.goodstein@intel.com>
Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Link: https://patch.msgid.link/20240702192118.6ad0a083f574.Ie41206c8ce4507fe26b991937f47e86c24ca7a31@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
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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 <mordechay.goodstein@intel.com>
Link: https://patch.msgid.link/20240702192118.c4093bc5b15e.I2ca8d006b67feeb866ac2017af7b741c9e06445a@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
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This implements synchronized time-travel mode which - using a special
application on a unix socket - lets multiple machines take part in a
time-travelling simulation together.
The protocol for the unix domain socket is defined in the new file
include/uapi/linux/um_timetravel.h.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
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