This patch accomplishes two things:
1. Makes simulate()'s GlobalSimLoopExitEvent a singleton reused
across calls. This is slightly more efficient than recreating
it every time.
2. Gives callers to simulate() (especially other simulators) a
foolproof way of knowing that the simulation period ended
successfully by hitting the limit event. They can call
getLimitEvent() and compare it to the return
value of simulate().
This change was motivated by an ongoing effort to integrate gem5
and SST, with SST as the master sim and gem5 as the slave sim.
We need the ability to lock event queues to enable device accesses
across threads. The serviceOne() method now takes a service lock prior
to handling a new event. By locking an event queue, a different
thread/eq can effectively execute in the context of the locked event
queue. To simplify temporary event queue migrations, this changeset
introduces the EventQueue::ScopedMigration class that unlocks the
current event queue, locks a new event queue, and updates the current
event queue variable.
In order to prevent deadlocks, event queues need to be released when
waiting on barriers. This is implemented using the
EventQueue::ScopedRelease class. An instance of this class is, for
example, used in the BaseGlobalEvent class to release the event queue
when waiting on the synchronization barrier.
The intended use for this functionality is when devices need to be
accessed across thread boundaries. For example, when fast-forwarding,
it might be useful to run devices and CPUs in separate threads. In
such a case, the CPU locks the device queue whenever it needs to
perform IO. This functionality is primarily intended for KVM.
Note: Migrating between event queues can lead to non-deterministic
timing. Use with extreme care!
--HG--
extra : rebase_source : 23e3a741a1fd73861d1339782dbbe1bc76285315
The global synchronization event used to be scheduled at
simQuantum. This prevented repeated entries into gem5 from Python as
it can be scheduled in the past. This changeset ensures that the first
global synchronization happens at curTick() + simQuantum instead.
There is a race between enabling asynchronous IO for a file descriptor
and IO events happening on that descriptor. A SIGIO won't normally be
delivered if an event is pending when asynchronous IO is
enabled. Instead, the signal will be raised the next time there is an
event on the FD. This changeset simulates a SIGIO by setting the
async_io flag when setting up asynchronous IO for an FD. This causes
the main event loop to poll all file descriptors to check for pending
IO. As a consequence of this, the old SIGALRM hack should no longer be
needed and is therefore removed.
2013-11-29 14:36:10 +01:00
Steve Reinhardt ext:(%2C%20Nilay%20Vaish%20%3Cnilay%40cs.wisc.edu%3E%2C%20Ali%20Saidi%20%3CAli.Saidi%40ARM.com%3E)
This patch adds support for simulating with multiple threads, each of
which operates on an event queue. Each sim object specifies which eventq
is would like to be on. A custom barrier implementation is being added
using which eventqs synchronize.
The patch was tested in two different configurations:
1. ruby_network_test.py: in this simulation L1 cache controllers receive
requests from the cpu. The requests are replied to immediately without
any communication taking place with any other level.
2. twosys-tsunami-simple-atomic: this configuration simulates a client-server
system which are connected by an ethernet link.
We still lack the ability to communicate using message buffers or ports. But
other things like simulation start and end, synchronizing after every quantum
are working.
Committed by: Nilay Vaish
HG changset 34e3295b0e39 introduced a check in the main simulation
loop that discards exit events that happen at the same tick as another
exit event. This was supposed to fix a problem where a simulation
script got confused by multiple exit events. This obviously breaks the
simulator since it can hide important simulation events, such as a
simulation failure, that happen at the same time as a non-fatal
simulation event.
When "-I" (maximum instruction number) and "-F" (fastforward instruction
number) are applied together, gem5 immediately exits after the cpu switching.
The reason is that multiple exit events may be generated in the same cycle by
Atomic CPU and inserted to mainEventQueue. However, mainEventQueue can only
serve one exit event in one cycle. Therefore, the rest exit events are left in
mainEventQueue without being descheduled or deleted, which causes gem5 exits
immediately after the system resumes by cpu switching.
This patch adds a _curTick variable to an eventq. This variable is updated
whenever an event is serviced in function serviceOne(), or all events upto
a particular time are processed in function serviceEvents(). This change
helps when there are eventqs that do not make use of curTick for scheduling
events.
The major thrust of this change is to limit the amount of code
duplication surrounding the code for these functions. This code also
adds two new message types called info and hack. Info is meant to be
less harsh than warn so people don't get confused and start thinking
that the simulator is broken. Hack is a way for people to add runtime
messages indicating that the simulator just executed a code "hack"
that should probably be fixed. The benefit of knowing about these
code hacks is that it will let people know what sorts of inaccuracies
or potential bugs might be entering their experiments. Finally, I've
added some flags to turn on and off these message types so command
line options can change them.
so things are organized in a more sensible manner. Take apart
finalInit and expose the individual functions which are now
called from python. Make checkpointing a bit easier to use.
--HG--
extra : convert_revision : f470ddabbb47103e7b4734ef753c40089f2dcd9d
