We currently use the traditional SI-like prefixes for to represent
binary multipliers in some contexts. This is ambiguous in many cases
since they overload the meaning of the SI prefix.
Here are some examples of commonly used in the industry:
* Storage vendors define 1 MB as 10**6 bytes
* Memory vendors define 1 MB as 2**20 bytes
* Network equipment treats 1Mbit/s as 10**6 bits/s
* Memory vendors define 1Mbit as 2**20 bits
In practice, this means that a FLASH chip on a storage bus uses
decimal prefixes, but that same flash chip on a memory bus uses binary
prefixes. It would also be reasonable to assume that the contents of a
1Mbit FLASH chip would take 0.1s to transfer over a 10Mbit Ethernet
link. That's however not the case due to different meanings of the
prefix.
The quantity 2MX is treated differently by gem5 depending on the unit
X:
* Physical quantities (s, Hz, V, A, J, K, C, F) use decimal prefixes.
* Interconnect and NoC bandwidths (B/s) use binary prefixes.
* Network bandwidths (bps) use decimal prefixes.
* Memory sizes and storage sizes (B) use binary prefixes.
Mitigate this ambiguity by consistently using the ISO/IEC/SI prefixes
for binary multipliers for parameters and comments where appropriate.
Change-Id: I2d24682d207830f3b7b0ad2ff82b55e082cccb32
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39576
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Implementation of a generic frequency-based sampling
compressor. The compressor goes through a sampling stage,
where no compression is done, and the values are simply
sampled for their frequencies. Then, after enough samples
have been taken, the compressor starts generating
compressed data.
Compression works by comparing chunks to the table of
most frequent values. In theory, a chunk that is present
in the frequency table has its value replaced by the
index of its respective entry in the table. In practice,
the value itself is stored because there is no straight-
forward way to acquire an index from an entry.
Finally, the index can be encoded so that the values
with highest frequency have smaller codeword representation.
Its Huffman coupling can be used similar to the approach
taken in "SC 2 : A Statistical Compression Cache Scheme".
Change-Id: Iae0ebda08e8c08f3b62930fd0fb7e818fd0d141f
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37335
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
The function was defined in a .cc file but marked as inline. gcc seems
to often figure out what it should do, but in clang it doesn't export
the function (since it's marked as inline), and during linking external
references, which don't have a local copy since it's not defined in the
.hh file, will fail.
This failure looks particularly odd because the funciton is virtual,
and so the failure is reported as being unable to compose the vtable
in places where the object is constructed, relatively obscure code
which is generated by the build system and obscured by templates from
an external code base (pybind11).
Change-Id: Ib51aefbf9005e4ca8dfebef32c5def472175f115
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37436
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
The compression factor of a block is measured according to the maximum
achievable compression ratio.
For example, if up to 4 blocks can co-allocate in a superblock, and
a cache line has 512 bits, the possible compression factors are 1
(uncompressed, <=512 bits), 2 (compressed, <=256 bits), 4 (compressed,
<=128 bits).
This is an approach similar to the one described in "Yet Another
Compressed Cache", by Sardashti et al.
Change-Id: I52ef36989f3eeef6fc8890132a57f995ef9c5258
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36581
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
When setting the size of a compressed block, its compressibility
needs to be recalculated based on that, so move such functionality
to be done after the block has been inserted, within setSizeBits.
As a side effect, insertBlock does not need to be overridden
anymore.
Change-Id: I608f876cd2110ac5e394ffad5b29941ba458ba91
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36580
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Data contractions happen when a block passes from a less compressed
(e.g., uncompressed) to a more compressed (e.g., compressed) state.
Some compaction methods enforce that a block can only be allocated
in a location matches an exact compression factor, thus on data
contractions such blocks must be moved to another location, or
they must be padded to fake a bigger size.
For compaction methods that do not have that limitation, performance
can be improved if the contracted block is moved to co-allocate with
another existing entry, since it frees up an entry.
Change-Id: I302bc561b897f9d3ce1426331fe4b5c2df76f4b5
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36578
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
When searching for victims of a data expansion a simple approach to
make room for the expanded block is to evict every co-allocatable
block. This, however, ignores replacement policies and tends to be
inefficient. Besides, some cache compaction policies do not allow
blocks that changed their compression ratio to be allocated in the
same location (e.g., Skewed Compressed Caches), so they must be
moved elsewhere.
The replacement policy approach asks the replacement policy which
block(s) would be the best to evict in order to make room for the
expanded block. The other approach, on the other hand, simply evicts
all co-allocated entries. In the case the replacement policy selects
the superblock of the block being expanded, we must make sure the
latter is not evicted/moved by mistake.
This patch also allows the user to select which approach they would
like to use.
Change-Id: Iae57cf26dac7218c51ff0169a5cfcf3d6f8ea28a
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36577
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Some cache techniques may need to move a block's metadata information
into another block. This must have some limitations to avoid mistakes:
- The destination entry must be invalid, otherwise the replacement
policy steps would be skipped.
- The source entry must be valid, otherwise there would be no point
in moving their metadata contents.
- The entries locations (set, way, offset...) must not be moved, since
they are fixed. The same principle is applied to the location specific
variables, such as the replacement pointer
Why it would be used:
For example, when using compression, and a block goes from uncompressed
to compressed state due to an overwrite, after the tag lookup
(sequential access) it can be decided whether to store the new data in
the old location, or, since we might have already found the block's co-
allocatable blocks, move it to co-allocate.
Other examples of techniques that could use this functionality are
Skewed Compressed Caches, and ZCaches.
Change-Id: I96e4f8cc8c992c4b01f315251d1a75d51c28692c
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36575
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
The create() method on Params structs usually instantiate SimObjects
using a constructor which takes the Params struct as a parameter
somehow. There has been a lot of needless variation in how that was
done, making it annoying to pass Params down to base classes. Some of
the different forms were:
const Params &
Params &
Params *
const Params *
Params const*
This change goes through and fixes up every constructor and every
create() method to use the const Params & form. We use a reference
because the Params struct should never be null. We use const because
neither the create method nor the consuming object should modify the
record of the parameters as they came in from the config. That would
make consuming them not idempotent, and make it impossible to tell what
the actual simulation configuration was since it would change from any
user visible form (config script, config.ini, dot pdf output).
Change-Id: I77453cba52fdcfd5f4eec92dfb0bddb5a9945f31
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35938
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Encapsulate this variable to facilitate polymorphism.
- The status enum was renamed to CoherenceBits, since it
lists the coherence bits supported by the CacheBlk.
- status was made protected and renamed to coherence since
it contains the coherence bits.
- Functions to set, clear and get the coherence bits were
created.
- To set a status bit, the block must be validated first.
This guarantees a constant flow and helps catching bugs.
As a side effect, some of the modified files contained long
lines, which had to be split.
Change-Id: I558cc51ac685d30b6bf298c78f86a6e24ff06973
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34960
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
The TaggedEntry class inherits from the ReplaceableEntry
class. Its purpose is to define a replaceable entry with
tagging attributes.
It has been created as a separate class because both the
replacement policies and the AbstractCacheEntry use
ReplaceableEntry, and do not need the tagging information
to perform their operations.
Change-Id: I24e87c865fc21c79dea7e488507a8cafc5223b39
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35698
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Encapsulate this variable to facilitate polymorphism.
- tickInserted was renamed to _tickInserted and was privatized.
- The insertion tick should always be set to the current tick,
and only on insertion; thus, its setter is not public and
does not take arguments.
- An additional function was created to get the age since of
the block relative to its insertion tick.
- There is no current need for a getter.
Change-Id: I81d4009abec5e9633e10f1e851e3a524553c98a4
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34958
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Encapsulate this variable to facilitate polymorphism.
- refCount was renamed to _refCount and was privatized.
- The reference count should only be reset at invalidation;
thus, its setter is not public.
- An additional function was created to increment the number
of references by 1.
Change-Id: Ibc8799a8dcb7c53c651de3eb1c9b86118a297b9d
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34957
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Make the tag variable private, so that every access to it must pass
through a getter and a setter. This protects it from being incorrectly
updated when there is no direct match between a tag and a data entry,
as is the case of sector, compressed, decoupled, and many other table
layouts.
As a side effect, a block matching function has been created, which
also depends directly on the mapping between tag and data entries.
Change-Id: I848a154404feb5cbcea8d0fd2509bf49e1d73bd0
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34955
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
This change replaces the __attribute__ syntax with the now standard [[]]
syntax. It also reorganizes compiler.hh so that all special macros have
some explanatory text saying what they do, and each attribute which has a
standard version can use that if available and what version of c++ it's
standard in is put in a comment.
Also, the requirements as far as where you put [[]] style attributes are
a little more strict than the old school __attribute__ style. The use of
the attribute macros was updated to fit these new, more strict
requirements.
Change-Id: Iace44306a534111f1c38b9856dc9e88cd9b49d2a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35219
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Allow all sub-compressors of BDI to be successful as long as
they are able to compress. Then, BDI's actual size threshold
acts as the cutting point.
This situation arises on any multi compressor; yet, generalizing
this assumption might be too bold.
Change-Id: Iec5057d16d4a7ba5fb573133a30ea10869bd67e0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33386
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
The size can be zero in special occasions, which would
generate divisions by zero. This patch expands the
stats to support them. It also fixes the compression
factor calculation in the Multi compressor.
As a side effect, now that zero sizes are handled, allow
the Zero compressor to generate it.
Change-Id: I9f7dee76576b09fdc9bef3e1f3f89be3726dcbd9
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33383
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
