configs: Use absolute import paths

Use absoluate import paths to be Python 3 compatible. This also
imports absolute_import from __future__ to ensure that Python 2.7
behaves the same way as Python 3.

Change-Id: Ica06ed95814e9cd3e768b3e1785075e36f6e56d0
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/16708
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

sim: Remove redundant buildEnv import

Change-Id: Id6bdbc0c988aa92b96e292cabc913e6b974f14bb
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>

mem: Split the hit_latency into tag_latency and data_latency

If the cache access mode is parallel, i.e. "sequential_access" parameter
is set to "False", tags and data are accessed in parallel. Therefore,
the hit_latency is the maximum latency between tag_latency and
data_latency. On the other hand, if the cache access mode is
sequential, i.e. "sequential_access" parameter is set to "True",
tags and data are accessed sequentially. Therefore, the hit_latency
is the sum of tag_latency plus data_latency.

Signed-off-by: Jason Lowe-Power <jason@lowepower.com>

mem: Deduce if cache should forward snoops

This patch changes how the cache determines if snoops should be
forwarded from the memory side to the CPU side. Instead of having a
parameter, the cache now looks at the port connected on the CPU side,
and if it is a snooping port, then snoops are forwarded. Less error
prone, and less parameters to worry about.

The patch also tidies up the CPU classes to ensure that their I-side
port is not snooping by removing overrides to the snoop request
handler, such that snoop requests will panic via the default
MasterPort implement

mem: Add an option to perform clean writebacks from caches

This patch adds the necessary commands and cache functionality to
allow clean writebacks. This functionality is crucial, especially when
having exclusive (victim) caches. For example, if read-only L1
instruction caches are not sending clean writebacks, there will never
be any spills from the L1 to the L2. At the moment the cache model
defaults to not sending clean writebacks, and this should possibly be
re-evaluated.

The implementation of clean writebacks relies on a new packet command
WritebackClean, which acts much like a Writeback (renamed
WritebackDirty), and also much like a CleanEvict. On eviction of a
clean block the cache either sends a clean evict, or a clean
writeback, and if any copies are still cached upstream the clean
evict/writeback is dropped. Similarly, if a clean evict/writeback
reaches a cache where there are outstanding MSHRs for the block, the
packet is dropped. In the typical case though, the clean writeback
allocates a block in the downstream cache, and marks it writable if
the evicted block was writable.

The patch changes the O3_ARM_v7a L1 cache configuration and the
default L1 caches in config/common/Caches.py

mem: Add explicit Cache subclass and make BaseCache abstract

Open up for other subclasses to BaseCache and transition to using the
explicit Cache subclass.

mem: Remove redundant is_top_level cache parameter

This patch takes the final step in removing the is_top_level parameter
from the cache. With the recent changes to read requests and write
invalidations, the parameter is no longer needed, and consequently
removed.

This also means that asymmetric cache hierarchies are now fully
supported (and we are actually using them already with L1 caches, but
no table-walker caches, connected to a shared L2).

mem: Allow read-only caches and check compliance

This patch adds a parameter to the BaseCache to enable a read-only
cache, for example for the instruction cache, or table-walker cache
(not for x86). A number of checks are put in place in the code to
ensure a read-only cache does not end up with dirty data.

A follow-on patch adds suitable read requests to allow a read-only
cache to explicitly ask for clean data.

arch, cpu: Do not forward snoops to table walker

This patch simplifies the overall CPU by changing the TLB caches such
that they do not forward snoops to the table walker port(s). Note that
only ARM and X86 are affected.

There is no reason for the ports to snoop as they do not actually take
any action, and from a performance point of view we are better of not
snooping more than we have to.

Should it at a later point be required to snoop for a particular TLB
design it is easy enough to add it back.

config: Update script to set cache line size on system

This patch changes the config scripts such that they do not set the
cache line size per cache instance, but rather for the system as a
whole.

config: Unify caches used in regressions and adjust L2 MSHRs

This patch unified the L1 and L2 caches used throughout the
regressions instead of declaring different, but very similar,
configurations in the different scripts.

The patch also changes the default L2 configuration to match what it
used to be for the fs and se scripts (until the last patch that
updated the regressions to also make use of the cache config). The
MSHRs and targets per MSHR are now set to a more realistic default of
20 and 12, respectively.

As a result of both the aforementioned changes, many of the regression
stats are changed. A follow-on patch will bump the stats.

config: Fix the cache class naming in regression scripts

This patch unifies the naming of the default L1 and L2 caches in the
regression configs to be in line with what is used in the se and fs
scripts.

config: Use shared cache config for regressions

This patch uses the common L1, L2 and IOCache configuration for the
regressions that all share the same cache parameters. There are a few
regressions that use a slightly different configuration (memtest,
o3-timing=mp, simple-atomic-mp and simple-timing-mp), and the latter
are not changed in this patch. They will be updated in a future patch.

The common cache configurations are changed to match the ones used in
the regressions, and are slightly changed with respect to what they
were. Hopefully this means we can converge on a common base
configuration, used both in the normal user configurations and
regressions.

As only regressions that shared the same cache configuration are
updated, no regressions are affected.

Mem: Use cycles to express cache-related latencies

This patch changes the cache-related latencies from an absolute time
expressed in Ticks, to a number of cycles that can be scaled with the
clock period of the caches. Ultimately this patch serves to enable
future work that involves dynamic frequency scaling. As an immediate
benefit it also makes it more convenient to specify cache performance
without implicitly assuming a specific CPU core operating frequency.

The stat blocked_cycles that actually counter in ticks is now updated
to count in cycles.

As the timing is now rounded to the clock edges of the cache, there
are some regressions that change. Plenty of them have very minor
changes, whereas some regressions with a short run-time are perturbed
quite significantly. A follow-on patch updates all the statistics for
the regressions.

Cache: add a response latency to the caches

In the current caches the hit latency is paid twice on a miss. This patch lets
a configurable response latency be set of the cache for the backward path.

O3: Remove hardcoded tgts_per_mshr in O3CPU.py.

There are two lines in O3CPU.py that set the dcache and icache
tgts_per_mshr to 20, ignoring any pre-configured value of tgts_per_mshr.
This patch removes these hardcoded lines from O3CPU.py and sets the default
L1 cache mshr targets to 20.

Mem: Fix issue with dirty block being lost when entire block transferred to non-cache.

This change fixes the problem for all the cases we actively use. If you want to try
more creative I/O device attachments (E.g. sharing an L2), this won't work. You
would need another level of caching between the I/O device and the cache
(which you actually need anyway with our current code to make sure writes
propagate). This is required so that you can mark the cache in between as
top level and it won't try to send ownership of a block to the I/O device.
Asserts have been added that should catch any issues.

X86: Add L1 caches for the TLB walkers.

Small L1 caches are connected to the TLB walkers when caches are used. This
allows them to participate in the coherence protocol properly.

python: Move more code into m5.util allow SCons to use that code.
Get rid of misc.py and just stick misc things in __init__.py
Move utility functions out of SCons files and into m5.util
Move utility type stuff from m5/__init__.py to m5/util/__init__.py
Remove buildEnv from m5 and allow access only from m5.defines
Rename AddToPath to addToPath while we're moving it to m5.util
Rename read_command to readCommand while we're moving it
Rename compare_versions to compareVersions while we're moving it.

mem: use single BadAddr responder per system.
Previously there was one per bus, which caused some coherence problems
when more than one decided to respond. Now there is just one on
the main memory bus. The default bus responder on all other buses
is now the downstream cache's cpu_side port. Caches no longer need
to do address range filtering; instead, we just have a simple flag
to prevent snoops from propagating to the I/O bus.

DMA: Add IOCache and fix bus bridge to optionally only send requests one
way so a cache can handle partial block requests for i/o devices.

Get rid of remaining traces of obsolete CoherenceProtocol object.

remove hit_latency and make latency do the right thing
set the latency parameter in terms of a latency
add caches to tsunami-simple configs

configs/common/Caches.py:
tests/configs/memtest.py:
tests/configs/o3-timing-mp.py:
tests/configs/o3-timing.py:
tests/configs/simple-atomic-mp.py:
tests/configs/simple-timing-mp.py:
tests/configs/simple-timing.py:
set the latency parameter in terms of a latency
configs/common/FSConfig.py:
give the bridge a default latency too
src/mem/cache/cache_builder.cc:
src/python/m5/objects/BaseCache.py:
remove hit_latency and make latency do the right thing
tests/configs/tsunami-simple-atomic-dual.py:
tests/configs/tsunami-simple-atomic.py:
tests/configs/tsunami-simple-timing-dual.py:
tests/configs/tsunami-simple-timing.py:
add caches to tsunami-simple configs

Add L2 cache option to fs.py --l2cache

factor out common run code from se.py and fs.py.

configs/example/fs.py:
factor out common code.
configs/example/se.py:
factor out common code