Mwait works as follows:
1. A cpu monitors an address of interest (monitor instruction)
2. A cpu calls mwait - this loads the cache line into that cpu's cache.
3. The cpu goes to sleep.
4. When another processor requests write permission for the line, it is
evicted from the sleeping cpu's cache. This eviction is forwarded to the
sleeping cpu, which then wakes up.
Committed by: Nilay Vaish <nilay@cs.wisc.edu>
This is a simple test program for the new mwait implemenation. It is uses
m5threads to create to threads of execution in syscall emulation mode that
interact using the mwait instruction.
Committed by: Nilay Vaish <nilay@cs.wisc.edu>
Fixes a bug where Minor drains in the midst of committing a
conditional store.
While committing a conditional store, lastCommitWasEndOfMacroop is true
(from the previous instruction) as we still haven't finished the conditional
store. If a drain occurs before the cache response, Minor would check just
lastCommitWasEndOfMacroop, which was true, and set drainState=DrainHaltFetch,
which increases the streamSeqNum. This caused the conditional store to be
squashed when the memory responded and it completed. However, to the memory
the store succeeded, while to the instruction sequence it never occurred.
In the case of an LLSC, the instruction sequence will replay the squashed
STREX, which will fail as the cache is no longer in LLSC. Then the
instruction sequence will loop back to a LDREX, which receives the updated
(incorrect) value.
Committed by: Nilay Vaish <nilay@cs.wisc.edu>
Ruby's functional accesses are not guaranteed to succeed as of now. While
this is not a problem for the protocols that are currently in the mainline
repo, it seems that coherence protocols for gpus rely on a backing store to
supply the correct data. The aim of this patch is to make this backing store
configurable i.e. it comes into play only when a particular option:
--access-backing-store is invoked.
The backing store has been there since M5 and GEMS were integrated. The only
difference is that earlier the system used to maintain the backing store and
ruby's copy was write-only. Sometime last year, we moved to data being
supplied supplied by ruby in SE mode simulations. And now we have patches on
the reviewboard, which remove ruby's copy of memory altogether and rely
completely on the system's memory to supply data. This patch adds back a
SimpleMemory member to RubySystem. This member is used only if the option:
access-backing-store is set to true. By default, the memory would not be
accessed.
This patch is the final in the series. The whole series and this patch in
particular were written with the aim of interfacing ruby's directory controller
with the memory controller in the classic memory system. This is being done
since ruby's memory controller has not being kept up to date with the changes
going on in DRAMs. Classic's memory controller is more up to date and
supports multiple different types of DRAM. This also brings classic and
ruby ever more close. The patch also changes ruby's memory controller to
expose the same interface.
This function was added when I had incorrectly arrived at the conclusion
that such a function can improve the chances of a functional read succeeding.
As was later realized, this is not possible in the current setup. While the
code using this function was dropped long back, this function was not. Hence
the patch.
This patch removes the data block present in the directory entry structure
of each protocol in gem5's mainline. Firstly, this is required for moving
towards common set of memory controllers for classic and ruby memory systems.
Secondly, the data block was being misused in several places. It was being
used for having free access to the physical memory instead of calling on the
memory controller.
From now on, the directory controller will not have a direct visibility into
the physical memory. The Memory Vector object now resides in the
Memory Controller class. This also means that some significant changes are
being made to the functional accesses in ruby.
In my opinion, it creates needless complications in rest of the code.
Also, this structure hinders the move towards common set of code for
physical memory controllers.
Both ruby and the system used to maintain memory copies. With the changes
carried for programmed io accesses, only one single memory is required for
fs simulations. This patch sets the copy of memory that used to reside
with the system to null, so that no space is allocated, but address checks
can still be carried out. All the memory accesses now source and sink values
to the memory maintained by ruby.
As of now DMASequencer inherits from the RubyPort class. But the code in
RubyPort class is heavily tailored for the CPU Sequencer. There are parts of
the code that are not required at all for the DMA sequencer. Moreover, the
next patch uses the dma sequencer for carrying out memory accesses for all the
io devices. Hence, it is better to have a leaner dma sequencer.
This changes the default ARM system to a Versatile Express-like system that supports
2GB of memory and PCI devices and updates the default kernels/file-systems for
AArch64 ARM systems (64-bit) to support up to 32GB of memory and PCI devices. Some
platforms that are no longer supported have been pruned from the configuration files.
In addition a set of 64-bit ARM regressions have been added to the regression system.
It is possible for the O3 CPU to consider itself drained and
later have a squashed instruction perform a writeback. This
patch re-adds tracking of in-flight instructions to prevent
falsely signaling a drained event.
IEW did not check the instQueue and memDepUnit to ensure
they were drained. This caused issues when drainSanityCheck()
did check those structures after asserting IEW was drained.
The bare-metal configuration option still configured memory with the old scheme
that no-longer works. This change unifies the code so there aren't any differences.
The checker can't verify timer registers, so it should just grab the version
from the executing CPU, otherwise it could get a larger value and diverge
execution.
This patch fixes a bug where a completing load or store which is also a
barrier can push a barrier into the store buffer without first checking
that there is a free slot.
The bug was not fatal but would print a warning that the store buffer
was full when inserting.
WriteInvalidate semantics depend on the unconditional writeback
or they won't complete. Also, there's no point in deferring snoops
on their MSHRs, as they don't get new data at the end of their life
cycle the way other transactions do.
Add comment in the cache about a minor inefficiency re: WriteInvalidate.
Since WriteInvalidate directly writes into the cache, it can
create tricky timing interleavings with reads and writes to the
same cache line that haven't yet completed. This patch ensures
that these requests, when completed, don't overwrite the newer
data from the WriteInvalidate.
This hook allows blocking emulated system calls to indicate
that they would block, but return control to the simulator
so that the simulation does not hang. The actual retry
functionality requires additional support, to be provided
in a future changeset.
Move the BufferArg classes that support syscall buffer args
(i.e., pointers into simulated user space) out of syscall_emul.hh
and into a new header syscall_emul_buf.hh so they are accessible
to emulated driver implementations.
Take the opportunity to add some comments as well.
The identifier SYS_getdents is not available on Mac OS X. Therefore, its use
results in compilation failure. It seems there is no straight forward way to
implement the system call getdents using readdir() or similar C functions.
Hence the commit 6709bbcf564d is being rolled back.
This patch fixes a few minor issues that caused link-time warnings
when using LTO, mainly for x86. The most important change is how the
syscall array is created. Previously gcc and clang would complain that
the declaration and definition types did not match. The organisation
is now changed to match how it is done for ARM, moving the code that
was previously in syscalls.cc into process.cc, and having a class
variable pointing to the static array.
With these changes, there are no longer any warnings using gcc 4.6.3
with LTO.
This patch changes how we turn time into UTC. Previously we
manipulated the TZ environment variable, but this has issues as the
strings that are manipulated could be tainted (see e.g. CERT
ENV34-C). Now we simply rely on the built-in gmtime function and avoid
touching getenv/setenv all together.
This patch bumps DRAMPower to commit
19433a6897ede4bbb19b06694faa8589b5a6569a which contains a small fix
for clang, and a work-around for LTO with gcc 4.6.
This patch adds the size of the DRAM device to the DRAM config. It
also compares the actual DRAM size (calculated using information from
the config) to the size defined in the system. If these two values do
not match gem5 will print a warning. In order to do correct DRAM
research the size of the memory defined in the system should match the
size of the DRAM in the config. The timing and current parameters
found in the DRAM configs are defined for a DRAM device with a
specific size and would differ for another device with a different
size.
Presently, the alignment checks in the mmap and mremap implementations
in syscall_emul.hh are wrong. The checks are implemented as:
if ((start % TheISA::PageBytes) != 0 ||
(length % TheISA::PageBytes) != 0) {
warn("mmap failing: arguments not page-aligned: "
"start 0x%x length 0x%x",
start, length);
return -EINVAL;
}
This checks that both the start and the length arguments of the mmap
syscall are checked for page-alignment. However, the POSIX specification says:
The off argument is constrained to be aligned and sized according to the value
returned by sysconf() when passed _SC_PAGESIZE or _SC_PAGE_SIZE. When MAP_FIXED
is specified, the application shall ensure that the argument addr also meets
these constraints. The implementation performs mapping operations over whole
pages. Thus, while the argument len need not meet a size or alignment
constraint, the implementation shall include, in any mapping operation, any
partial page specified by the range [pa,pa+len).
So the length parameter should not be checked for page-alignment. By contrast,
the current implementation fails to check the offset argument, which must be
page aligned.
Committed by: Nilay Vaish <nilay@cs.wisc.edu>
Change mmap fixed address request to return an error if the mapping is
impossible due to conflict instead of what I believe used to be silent
corruption.
Committed by: Nilay Vaish <nilay@cs.wisc.edu>
On exit_group syscall, we used to exit the simulator. But now we will only
halt the execution of threads that belong to the group.
Committed by: Nilay Vaish <nilay@cs.wisc.edu>
This patch updates fputils to the latest revision (6a47fd8358) from
the upstream repository (github.com/andysan/fputils). Most notably,
this includes changes that export a limited set of 64-bit float
manipulation and avoids a warning about unused 64-bit floats in clang.
