https://github.com/ilyakurdyukov/e2k-ports

Performance patches and build fixes for Elbrus 2000 (e2k) architecture.
https://github.com/ilyakurdyukov/e2k-ports

e2k elbrus patches ports

Last synced: 26 days ago
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Performance patches and build fixes for Elbrus 2000 (e2k) architecture.

• Host: GitHub
• URL: https://github.com/ilyakurdyukov/e2k-ports
• Owner: ilyakurdyukov
• Created: 2021-03-13T12:55:45.000Z (almost 4 years ago)
• Default Branch: main
• Last Pushed: 2024-08-05T16:54:43.000Z (4 months ago)
• Last Synced: 2024-08-05T19:47:41.027Z (4 months ago)
• Topics: e2k, elbrus, patches, ports
• Homepage:
• Size: 771 KB
• Stars: 41
• Watchers: 8
• Forks: 5
• Open Issues: 6
• Metadata Files:
  • Readme: README.md

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• awesome-e2k - Патчи на производительность и исправления ошибок сборки

README

        
## e2k-ports

Performance patches and build fixes for Elbrus (e2k) architecture.

This is my personal repository so that patches won't get lost.

### Elbrus porting cheat sheet:

Elbrus 2000 (aka e2k) is a 64-bit little-endian architecture.  

The compiler is mostly GCC compatible (defines `__GNUC__`), EDG frontend.

#### detection

- shell: `uname -m` returns `e2k`

- cmake: `if({CMAKE_SYSTEM_PROCESSOR} STREQUAL "e2k")`

- C preprocessor: `if defined(__e2k__)`

- compiler version: if `__LCC__ = 125` and `__LCC_MINOR__ = 9` then it's "LCC 1.25.09"

- architecture version: defined in `__iset__` (less than 3 is obsolete, 6 is the latest at the moment)

#### intrinsics

- MMX, SSE2, SSSE3, SSE4.1* - native support

- AVX, AVX2 - supported, but not recommended, uses too much CPU registers

- SSE4.2 and _mm_dp_ps (from SSE4.1) - emulated, slow, do not use

The compiler enables MMX to AVX2 support by default, pass `-mno-avx` (`-mno-sse4.2`) if code depends on the presence of macros (e.g. `#if defined(__AVX2__)`).

#### builtins

- __sync*, __atomic* - supported by the compiler

- count leading/trailing zeros - supported (__builtin_clz, __builtin_ctz)

- memory fence - supported (need to include `x86intrin.h` first)

    - __builtin_ia32_mfence, __builtin_ia32_lfence, __builtin_ia32_sfence

#### cpuid

Use compile time CPU detection, select the best SIMD up to SSE4.1.

#### rdtsc

```c

#include 

uint64_t time = __rdtsc();

// same: unsigned aux; uint64_t time = __rdtscp(&aux);

```

#### useful pragmas

`_Pragma("name")` - to use from macros.

Use before the loop:

- `#pragma ivdep` - ignore data dependencies inside the loop

- `#pragma unroll(n)` - unroll cycle N times

#### restrict

Using the `restrict` keyword is good for performance, but note that it is ignored by the LCC if you're using vector load/store intrinsics such as `_mm_load_si128()`. For code with vector intrinsics use `#pragma ivdep`.

#### makecontext

Instead of `makecontext(ctx, ...)` use `makecontext_e2k(ctx, ...)`, returns a negative integer on error. Allocates extra resources that need to be freed using `freecontext_e2k(ctx)`.

#### nop

Use `__asm__ __volatile__ ("nop")` or `_mm_pause()` for a little delay.

#### clearing the instruction cache

The GNUC standard function `__clear_cache(char *begin, char *end)` works correctly since LCC 1.25.18, LCC 1.26.04.

This function is available in previous versions, but does nothing. 

#### inline

If it's crucial to performance, then use `__attribute__((__always_inline__)) inline` rather than just `inline`. Because when using large or complicated inline functions, the LCC compiler may decide not to inline them. 

#### avoid if possible

The GNUC C extension [Labels as Values](https://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html) is available in the LCC, but performance is worse than using a simple switch/case.

The GNUC [Vector Extension](https://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html) is also available in LCC, but poorly implemented and its performance is very bad.