RISC-V was the only major architecture without a get_L2_size() /
blas_set_parameter() implementation, so the GEMM cache-blocking parameters
(P/Q/R) were fixed at compile time regardless of the actual L2 cache size.
Because the blocking is now derived from the L2 cache detected at runtime
rather than a fixed compile-time constant, future RISC-V cores - which are
arriving with progressively larger and more varied L2 caches - get more
optimal blocking automatically, and the port gains the same runtime-tuning
hook x86 and LoongArch already use.
This adds, under ARCH_RISCV64:
- get_L2_size(): reads the level-2 (unified) cache size from Linux sysfs
(/sys/devices/system/cpu/cpu0/cache/index*/{level,size}); RISC-V has no
architectural cache-size query like x86 CPUID or LoongArch CPUCFG. Falls
back to 512 KB when sysfs is unavailable.
- blas_set_parameter(): scales each precision's packed-A dimension P from the
detected L2. The base blocking and the reference cache size come from the
active core's own param.h block (*_DEFAULT_P_BASE, RISCV_L2_REFERENCE_KB),
so the function carries no core-specific constants and is a no-op for cores
that do not opt in. Q and R keep their param.h defaults.
- driver/others/memory.c and common_macro.h: add ARCH_RISCV64 to the existing
architecture lists that call blas_set_parameter() and declare the runtime
parameter variables (sgemm_p, dgemm_p, ...).
- param.h RISCV64_ZVL256B: declares the per-core base blocking + reference and
maps SGEMM/DGEMM/CGEMM/ZGEMM DEFAULT_P to the runtime variables for static
builds; DYNAMIC_ARCH keeps the literals, since kernel/setparam-ref.c
init_parameter() initialises the gotoblas table from these macros and
blas_set_parameter() is not called on the dynamic path.
Only RISCV64_ZVL256B opts in so far; its base + reference are tuned on the
SpaceMiT X60, where a 512 KB L2 reproduces the stock blocking, so this is
performance-neutral on current hardware. Verified: a static RISCV64_ZVL256B
build reproduces the stock 128/128/16384 (SGEMM) and 64/128/8192 (DGEMM)
blocking; a DYNAMIC_ARCH build compiles cleanly (per-core setparam-ref objects
build without error); and get_L2_size() reads the correct size on both a
SpaceMiT X60 (512 KB L2) and a SiFive U74 / VisionFive 2 (2 MB L2).
The warning was:
```
/home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/driver/others/memory.c: At top level:
/home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/driver/others/memory.c:2565:14: warning: 'alloc_hugetlb' defined but not used [-Wunused-function]
2565 | static void *alloc_hugetlb(void *address){
| ^~~~~~~~~~~~~
```
The added define is the same as is already present in the TLS part of
`memory.c`. This follows up on gh-4681.
The warning was:
```
[4339/5327] Building C object driver/others/CMakeFiles/driver_others.dir/memory.c.o
/home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/driver/others/memory.c: In function 'blas_shutdown':
/home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/driver/others/memory.c:3257:10: warning: passing argument 1 of 'free' discards 'volatile' qualifier from pointer target type [-Wdiscarded-qualifiers]
3257 | free(newmemory);
| ^~~~~~~~~
In file included from /home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/common.h:83,
from /home/rgommers/code/pixi-dev-scipystack/openblas/OpenBLAS/driver/others/memory.c:74:
/home/rgommers/code/pixi-dev-scipystack/openblas/.pixi/envs/default/x86_64-conda-linux-gnu/sysroot/usr/include/stdlib.h:482:25: note: expected 'void *' but argument is of type 'volatile struct newmemstruct *'
482 | extern void free (void *__ptr) __THROW;
| ~~~~~~^~~~~
```
The use of `volatile` for `newmemstruct` seems on purpose, and there are
more such constructs in this file. The warning appeared after gh-4451
and is correct. The `free` prototype doesn't expect a volatile pointer,
hence this change adds a cast to silence the warning.
Nathan Goldbaum