mirror of https://github.com/torvalds/linux.git
138 lines
4.3 KiB
C
138 lines
4.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* x86-optimized CRC32 functions
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*
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* Copyright (C) 2008 Intel Corporation
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* Copyright 2012 Xyratex Technology Limited
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* Copyright 2024 Google LLC
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*/
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#include "crc-pclmul-template.h"
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static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_crc32);
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static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_pclmulqdq);
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static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_vpclmul_avx512);
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DECLARE_CRC_PCLMUL_FUNCS(crc32_lsb, u32);
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static inline u32 crc32_le_arch(u32 crc, const u8 *p, size_t len)
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{
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CRC_PCLMUL(crc, p, len, crc32_lsb, crc32_lsb_0xedb88320_consts,
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have_pclmulqdq);
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return crc32_le_base(crc, p, len);
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}
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#ifdef CONFIG_X86_64
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#define CRC32_INST "crc32q %1, %q0"
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#else
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#define CRC32_INST "crc32l %1, %0"
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#endif
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/*
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* Use carryless multiply version of crc32c when buffer size is >= 512 to
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* account for FPU state save/restore overhead.
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*/
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#define CRC32C_PCLMUL_BREAKEVEN 512
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asmlinkage u32 crc32c_x86_3way(u32 crc, const u8 *buffer, size_t len);
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static inline u32 crc32c_arch(u32 crc, const u8 *p, size_t len)
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{
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size_t num_longs;
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if (!static_branch_likely(&have_crc32))
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return crc32c_base(crc, p, len);
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if (IS_ENABLED(CONFIG_X86_64) && len >= CRC32C_PCLMUL_BREAKEVEN &&
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static_branch_likely(&have_pclmulqdq) && likely(irq_fpu_usable())) {
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/*
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* Long length, the vector registers are usable, and the CPU is
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* 64-bit and supports both CRC32 and PCLMULQDQ instructions.
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* It is worthwhile to divide the data into multiple streams,
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* CRC them independently, and combine them using PCLMULQDQ.
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* crc32c_x86_3way() does this using 3 streams, which is the
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* most that x86_64 CPUs have traditionally been capable of.
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*
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* However, due to improved VPCLMULQDQ performance on newer
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* CPUs, use crc32_lsb_vpclmul_avx512() instead of
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* crc32c_x86_3way() when the CPU supports VPCLMULQDQ and has a
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* "good" implementation of AVX-512.
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*
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* Future work: the optimal strategy on Zen 3--5 is actually to
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* use both crc32q and VPCLMULQDQ in parallel. Unfortunately,
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* different numbers of streams and vector lengths are optimal
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* on each CPU microarchitecture, making it challenging to take
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* advantage of this. (Zen 5 even supports 7 parallel crc32q, a
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* major upgrade.) For now, just choose between
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* crc32c_x86_3way() and crc32_lsb_vpclmul_avx512(). The latter
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* is needed anyway for crc32_le(), so we just reuse it here.
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*/
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kernel_fpu_begin();
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if (static_branch_likely(&have_vpclmul_avx512))
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crc = crc32_lsb_vpclmul_avx512(crc, p, len,
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crc32_lsb_0x82f63b78_consts.fold_across_128_bits_consts);
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else
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crc = crc32c_x86_3way(crc, p, len);
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kernel_fpu_end();
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return crc;
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}
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/*
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* Short length, XMM registers unusable, or the CPU is 32-bit; but the
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* CPU supports CRC32 instructions. Just issue a single stream of CRC32
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* instructions inline. While this doesn't use the CPU's CRC32
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* throughput very well, it avoids the need to combine streams. Stream
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* combination would be inefficient here.
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*/
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for (num_longs = len / sizeof(unsigned long);
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num_longs != 0; num_longs--, p += sizeof(unsigned long))
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asm(CRC32_INST : "+r" (crc) : ASM_INPUT_RM (*(unsigned long *)p));
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if (sizeof(unsigned long) > 4 && (len & 4)) {
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asm("crc32l %1, %0" : "+r" (crc) : ASM_INPUT_RM (*(u32 *)p));
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p += 4;
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}
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if (len & 2) {
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asm("crc32w %1, %0" : "+r" (crc) : ASM_INPUT_RM (*(u16 *)p));
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p += 2;
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}
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if (len & 1)
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asm("crc32b %1, %0" : "+r" (crc) : ASM_INPUT_RM (*p));
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return crc;
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}
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#define crc32_be_arch crc32_be_base /* not implemented on this arch */
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#define crc32_mod_init_arch crc32_mod_init_arch
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static void crc32_mod_init_arch(void)
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{
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if (boot_cpu_has(X86_FEATURE_XMM4_2))
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static_branch_enable(&have_crc32);
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if (boot_cpu_has(X86_FEATURE_PCLMULQDQ)) {
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static_branch_enable(&have_pclmulqdq);
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if (have_vpclmul()) {
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if (have_avx512()) {
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static_call_update(crc32_lsb_pclmul,
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crc32_lsb_vpclmul_avx512);
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static_branch_enable(&have_vpclmul_avx512);
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} else {
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static_call_update(crc32_lsb_pclmul,
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crc32_lsb_vpclmul_avx2);
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}
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}
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}
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}
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static inline u32 crc32_optimizations_arch(void)
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{
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u32 optimizations = 0;
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if (static_key_enabled(&have_crc32))
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optimizations |= CRC32C_OPTIMIZATION;
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if (static_key_enabled(&have_pclmulqdq))
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optimizations |= CRC32_LE_OPTIMIZATION;
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return optimizations;
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}
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