Change drcachesim default to core_serial for a much improved schedule #6949
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derekbruening
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Oct 15, 2024
Adds a new interface trace_analysis_tool::preferred_shard_type() to
the drmemtrace framework to allow tools to request core-sharded
operation.
The cache simulator, TLB simulator, and schedule_stats tools override
the new interface to request core-sharded mode.
Unfortunately, it is not easy to detect core-sharded-on-disk traces in
the launcher, so the user must now pass `-no_core_sharded` when using
such traces with core-sharded-preferring tools to avoid the trace
being re-scheduled yet again. Documentation for this is added and it
is turned into a fatal error since this re-scheduling there is almost
certainly user error.
In the launcher, if all tools prefer core-sharded, and the user did
not specify -no_core_sharded, core-sharded (or core-serial) mode is
enabled, with a -verbose 1+ message.
```
$ bin64/drrun -stderr_mask 0 -t drcachesim -indir ../src/clients/drcachesim/tests/drmemtrace.threadsig.x64.tracedir/ -verbose 1 -tool schedule_stats:cache_simulator
Enabling -core_serial as all tools prefer it
<...>
Schedule stats tool results:
Total counts:
4 cores
8 threads: 1257600, 1257602, 1257599, 1257603, 1257598, 1257604, 1257596, 1257601
638938 instructions
<...>
Core #0 schedule: AEA_A_
Core #1 schedule: BH_
Core #2 schedule: CG
Core #3 schedule: DF_
<...>
Cache simulation results:
Core #0 (traced CPU(s): #0)
L1I0 (size=32768, assoc=8, block=64, LRU) stats:
Hits: 123,659
<...>
```
If at least one tool prefers core-sharded but others do not, a
-verbose 1+ message suggests running with an explicit -core_sharded.
```
$ bin64/drrun -stderr_mask 0 -t drcachesim -indir ../src/clients/drcachesim/tests/drmemtrace.threadsig.x64.tracedir/ -verbose 1 -tool cache_simulator:basic_counts
Some tool(s) prefer core-sharded: consider re-running with -core_sharded or -core_serial enabled for best results.
```
Reduces the scheduler queue diagnostics by 5x as they seem too
frequent in short runs.
Updates the documentation to mention the new defaults.
Updates numerous drcachesim test output templates.
Keeps a couple of tests using thread-sharded by passing -no_core_serial.
Fixes #6949
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Today the drcachesim default is still the old static round-robin assignment of threads to cores. We should change the default to be core_serial to use the scheduler. There are complexities preventing us from removing the old static schedule, though: if you want to run another tool at the same time that doesn't want core-sharded, it seems like we should still support that.
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