1GB pages for the TT give a small performance bump (`./stockfish speedtest 256 32000`):
master:
Nodes/second : 230514479
patch
Nodes/second : 237997728
With a large enough TT there is still dTLB thrashing with 2MB pages. 1GB pages reduces that and makes page table walks a bit faster (they're shorter, and there's fewer PTEs, which fits better in cache). `madvise` won't give you huge pages, only large pages, so we use mmap here.
We guard the huge page attempt to x86 + at least 8 huge pages per NUMA node, to avoid memory oversubscription when for example running with a 1.1 GB hash. Additionally, we change the TT clearing slightly so that the pages are better distributed across NUMA nodes.
Data from Torom:
master:
Nodes/second : 43524292
patch:
Nodes/second : 44080034
Data on an 8-thread Emerald Rapids VM:
./stockfish speedtest 8 65536
Baseline speedtest (2MB huge pages):
Nodes/second : 7366232
Nodes/second : 7262794
Nodes/second : 7355431
Nodes/second : 7318777
Baseline speedtest (1GB huge pages):
Nodes/second : 7541027
Nodes/second : 7572720
Nodes/second : 7550268
Nodes/second : 7538925
closes https://github.com/official-stockfish/Stockfish/pull/6681
No functional change
Even though this failed with non regression bounds on fishtest, merging
it as is to improve the current situation.
Failed Non Regression:
https://tests.stockfishchess.org/tests/view/6988814db0f3ca5200aafb50
LLR: -2.94 (-2.94,2.94) <-1.75,0.25>
Total: 185792 W: 48109 L: 48565 D: 89118
Ptnml(0-2): 553, 21228, 49811, 20730, 574
Previously we had code similar to this
```
alignas(64) std::uint8_t foo[1024];
const auto* int_ptr = reinterpret_cast<const std::int32_t*>(foo);
```
Which is a strict aliasing violation once we dereference int_ptr, which
invokes UB and causes newer gcc version to emit incorrect code.
fixes https://github.com/official-stockfish/Stockfish/issues/6598
fixes https://github.com/official-stockfish/Stockfish/issues/4932
This violation was introduced in PR #3287 and merged in commit 23c385e.
Due to aggressive compiler optimizations, users may need to include
CXXFLAGS=-fno-strict-aliasing as a build argument to ensure a correctly
functioning binary.
Also thanks to @anematode for writing parts of this and realizing this
strict aliasing violation.
closes https://github.com/official-stockfish/Stockfish/pull/6599
Bench: 2668754
Co-Authored-By: Timothy Herchen <timothy.herchen@gmail.com>
This enables different Stockfish processes that use the same weights to use the
same memory. The approach establishes equivalence by memory content, and is
compatible with NUMA replication. The benefit of sharing is reduced memory usage
and a speedup thanks to improved (inter-process) caching of the network in the
CPUs cache, and thus reduced bandwidth usage to main memory. Even though this
change doesn't benefit a user running a single process, this helps on fishtest
or e.g. for Lichess, when multiple games run concurrently, or multiple
positions are analyzed in parallel.
This concept was probably first introduced in the Monty engine
(https://github.com/official-monty/Monty/pull/62), after a discussion in
https://github.com/official-stockfish/fishtest/issues/2077 on the issue of
memory pressure. Measurements based on Torch
(https://github.com/user-attachments/files/21386224/verbatim.pdf) further
suggested that large gains were possible. Multiple other engines have
adopted this 'verbatim' format as well.
The implementation here adds the flexibility needed for SF, for example, retains
the ability to bundle compressed networks with the binary, to load nets by uci
option, and to distribute the shared nets to the proper NUMA region. This
flexibility comes with a fair amount of complexity in the implementation, such
as OS specific code, and fallback code.
For most users this should be transparent. However, for example, those running
docker containers should ensure the `--ipc` flag is set correctly, and
`--shm-size` is sufficiently large.
The benefits of this patch significantly depend on hardware, with systems with
many cores and a large (O(150MB), the net size) L3 cache benefitting typically
most. On such systems SF speedups (as measured via nps playing games with
large concurrency but just 1 thread) can be 38%, which results in master vs.
patch Elo which gains about 25 Elo.
```
# PLAYER : RATING ERROR POINTS PLAYED (%)
1 shared_memoryPR : 24.8 1.9 39432.0 73728 53
2 master : 0.0 ---- 34296.0 73728 47
```
In a multithreaded setup, where weights are already shared, that benefit is smaller,
for example on the same HW as above, but with 8t for each side.
```
# PLAYER : RATING ERROR POINTS PLAYED (%)
1 shared_memoryPR : 5.2 3.5 9351.0 18432 51
2 master : 0.0 ---- 9081.0 18432 49
```
On fishtest with a typical hardware mix of our contributors, the following was measured:
STC, 60k games
https://tests.stockfishchess.org/tests/view/69074a49ea4b268f1fac236c
Elo: 4.69 ± 1.4 (95%) LOS: 100.0%
Total: 60000 W: 16085 L: 15275 D: 28640
Ptnml(0-2): 154, 6440, 16053, 7148, 205
nElo: 9.38 ± 2.8 (95%) PairsRatio: 1.12
To verify correctness with a single process on a NUMA architecture,
speedtest was used, confirming near equivalence:
```
master: Average (over 10): 296236186
shared_memory: Average (over 10): 295769332
```
Currently, using large pages for the shared network weights is not always possible,
which can lead to a small slowdown (1-2%), in case a single process is run.
closes https://github.com/official-stockfish/Stockfish/pull/6173
No functional change
Co-authored-by: disservin <disservin.social@gmail.com>
Co-authored-by: Joost VandeVondele <Joost.VandeVondele@gmail.com>
`speedtest [threads] [hash_MiB] [time_s]`. `threads` default to system concurrency. `hash_MiB` defaults to `threads*128`. `time_s` defaults to 150.
Intended to be used with default parameters, as a stable hardware benchmark.
Example:
```
C:\dev\stockfish-master\src>stockfish.exe speedtest
Stockfish dev-20240928-nogit by the Stockfish developers (see AUTHORS file)
info string Using 16 threads
Warmup position 3/3
Position 258/258
===========================
Version : Stockfish dev-20240928-nogit
Compiled by : g++ (GNUC) 13.2.0 on MinGW64
Compilation architecture : x86-64-vnni256
Compilation settings : 64bit VNNI BMI2 AVX2 SSE41 SSSE3 SSE2 POPCNT
Compiler __VERSION__ macro : 13.2.0
Large pages : yes
User invocation : speedtest
Filled invocation : speedtest 16 2048 150
Available processors : 0-15
Thread count : 16
Thread binding : none
TT size [MiB] : 2048
Hash max, avg [per mille] :
single search : 40, 21
single game : 631, 428
Total nodes searched : 2099917842
Total search time [s] : 153.937
Nodes/second : 13641410
```
-------------------------------
Small unrelated tweaks:
- Network verification output is now handled as a callback.
- TT hashfull queries allow specifying maximum entry age.
closes https://github.com/official-stockfish/Stockfish/pull/5354
No functional change
- Capitalize comments
- Reformat multi-lines comments to equalize the widths of the lines
- Try to keep the width of comments around 85 characters
- Remove periods at the end of single-line comments
closes https://github.com/official-stockfish/Stockfish/pull/5469
No functional change
Previously, we had two type aliases, LargePagePtr and AlignedPtr, which
required manually initializing the aligned memory for the pointer.
The new helpers:
- make_unique_aligned
- make_unique_large_page
are now available for allocating aligned memory (with large pages). They
behave similarly to std::make_unique, ensuring objects allocated with
these functions follow RAII.
The old approach had issues with initializing non-trivial types or
arrays of objects. The evaluation function of the network is now a
unique pointer to an array instead of an array of unique pointers.
Memory related functions have been moved into memory.h
Passed High Hash Pressure Test Non-Regression STC:
https://tests.stockfishchess.org/tests/view/665b2b36586058766677cfd2
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 476992 W: 122426 L: 122677 D: 231889
Ptnml(0-2): 1145, 51027, 134419, 50744, 1161
Failed Normal Non-Regression STC:
https://tests.stockfishchess.org/tests/view/665b2997586058766677cfc8
LLR: -2.94 (-2.94,2.94) <-1.75,0.25>
Total: 877312 W: 225233 L: 226395 D: 425684
Ptnml(0-2): 2110, 94642, 246239, 93630, 2035
Probably a fluke since there shouldn't be a real slowndown and it has also
passed the high hash pressure test.
closes https://github.com/official-stockfish/Stockfish/pull/5332
No functional change
