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[92.145.124.62]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-424c838bef4sm24669765e9.46.2024.06.26.06.07.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Jun 2024 06:07:56 -0700 (PDT) From: Alexandre Ghiti To: Jonathan Corbet , Paul Walmsley , Palmer Dabbelt , Albert Ou , Andrea Parri , Nathan Chancellor , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng , Arnd Bergmann , Leonardo Bras , Guo Ren , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org Cc: Alexandre Ghiti , Andrea Parri Subject: [PATCH v2 04/10] riscv: Improve amocas.X use in cmpxchg() Date: Wed, 26 Jun 2024 15:03:41 +0200 Message-Id: <20240626130347.520750-5-alexghiti@rivosinc.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240626130347.520750-1-alexghiti@rivosinc.com> References: <20240626130347.520750-1-alexghiti@rivosinc.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit cmpxchg() uses amocas.X instructions from Zacas and Zabha but still uses the LR/SC acquire/release semantics which require barriers. Let's improve that by using proper amocas acquire/release semantics in order to avoid any of those barriers. Suggested-by: Andrea Parri Signed-off-by: Alexandre Ghiti --- arch/riscv/include/asm/cmpxchg.h | 60 ++++++++++++++++++-------------- 1 file changed, 33 insertions(+), 27 deletions(-) diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h index b9a3fdcec919..3c65b00a0d36 100644 --- a/arch/riscv/include/asm/cmpxchg.h +++ b/arch/riscv/include/asm/cmpxchg.h @@ -105,7 +105,9 @@ * indicated by comparing RETURN with OLD. */ -#define __arch_cmpxchg_masked(sc_sfx, cas_sfx, prepend, append, r, p, o, n) \ +#define __arch_cmpxchg_masked(sc_sfx, cas_sfx, \ + sc_prepend, sc_append, \ + r, p, o, n) \ ({ \ __label__ no_zacas, zabha, end; \ \ @@ -129,7 +131,7 @@ no_zacas:; \ ulong __rc; \ \ __asm__ __volatile__ ( \ - prepend \ + sc_prepend \ "0: lr.w %0, %2\n" \ " and %1, %0, %z5\n" \ " bne %1, %z3, 1f\n" \ @@ -137,7 +139,7 @@ no_zacas:; \ " or %1, %1, %z4\n" \ " sc.w" sc_sfx " %1, %1, %2\n" \ " bnez %1, 0b\n" \ - append \ + sc_append \ "1:\n" \ : "=&r" (__retx), "=&r" (__rc), "+A" (*(__ptr32b)) \ : "rJ" ((long)__oldx), "rJ" (__newx), \ @@ -150,9 +152,7 @@ no_zacas:; \ zabha: \ if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \ __asm__ __volatile__ ( \ - prepend \ " amocas" cas_sfx " %0, %z2, %1\n" \ - append \ : "+&r" (r), "+A" (*(p)) \ : "rJ" (n) \ : "memory"); \ @@ -160,7 +160,9 @@ zabha: \ end:; \ }) -#define __arch_cmpxchg(lr_sfx, sc_cas_sfx, prepend, append, r, p, co, o, n) \ +#define __arch_cmpxchg(lr_sfx, sc_sfx, cas_sfx, \ + sc_prepend, sc_append, \ + r, p, co, o, n) \ ({ \ __label__ zacas, end; \ register unsigned int __rc; \ @@ -172,12 +174,12 @@ end:; \ } \ \ __asm__ __volatile__ ( \ - prepend \ + sc_prepend \ "0: lr" lr_sfx " %0, %2\n" \ " bne %0, %z3, 1f\n" \ - " sc" sc_cas_sfx " %1, %z4, %2\n" \ + " sc" sc_sfx " %1, %z4, %2\n" \ " bnez %1, 0b\n" \ - append \ + sc_append \ "1:\n" \ : "=&r" (r), "=&r" (__rc), "+A" (*(p)) \ : "rJ" (co o), "rJ" (n) \ @@ -187,9 +189,7 @@ end:; \ zacas: \ if (IS_ENABLED(CONFIG_RISCV_ISA_ZACAS)) { \ __asm__ __volatile__ ( \ - prepend \ - " amocas" sc_cas_sfx " %0, %z2, %1\n" \ - append \ + " amocas" cas_sfx " %0, %z2, %1\n" \ : "+&r" (r), "+A" (*(p)) \ : "rJ" (n) \ : "memory"); \ @@ -197,7 +197,8 @@ zacas: \ end:; \ }) -#define _arch_cmpxchg(ptr, old, new, sc_sfx, prepend, append) \ +#define _arch_cmpxchg(ptr, old, new, sc_sfx, cas_sfx, \ + sc_prepend, sc_append) \ ({ \ __typeof__(ptr) __ptr = (ptr); \ __typeof__(*(__ptr)) __old = (old); \ @@ -206,22 +207,24 @@ end:; \ \ switch (sizeof(*__ptr)) { \ case 1: \ - __arch_cmpxchg_masked(sc_sfx, ".b" sc_sfx, \ - prepend, append, \ - __ret, __ptr, __old, __new); \ + __arch_cmpxchg_masked(sc_sfx, ".b" cas_sfx, \ + sc_prepend, sc_append, \ + __ret, __ptr, __old, __new); \ break; \ case 2: \ - __arch_cmpxchg_masked(sc_sfx, ".h" sc_sfx, \ - prepend, append, \ - __ret, __ptr, __old, __new); \ + __arch_cmpxchg_masked(sc_sfx, ".h" cas_sfx, \ + sc_prepend, sc_append, \ + __ret, __ptr, __old, __new); \ break; \ case 4: \ - __arch_cmpxchg(".w", ".w" sc_sfx, prepend, append, \ - __ret, __ptr, (long), __old, __new); \ + __arch_cmpxchg(".w", ".w" sc_sfx, ".w" cas_sfx, \ + sc_prepend, sc_append, \ + __ret, __ptr, (long), __old, __new); \ break; \ case 8: \ - __arch_cmpxchg(".d", ".d" sc_sfx, prepend, append, \ - __ret, __ptr, /**/, __old, __new); \ + __arch_cmpxchg(".d", ".d" sc_sfx, ".d" cas_sfx, \ + sc_prepend, sc_append, \ + __ret, __ptr, /**/, __old, __new); \ break; \ default: \ BUILD_BUG(); \ @@ -230,16 +233,19 @@ end:; \ }) #define arch_cmpxchg_relaxed(ptr, o, n) \ - _arch_cmpxchg((ptr), (o), (n), "", "", "") + _arch_cmpxchg((ptr), (o), (n), "", "", "", "") #define arch_cmpxchg_acquire(ptr, o, n) \ - _arch_cmpxchg((ptr), (o), (n), "", "", RISCV_ACQUIRE_BARRIER) + _arch_cmpxchg((ptr), (o), (n), "", ".aq", \ + "", RISCV_ACQUIRE_BARRIER) #define arch_cmpxchg_release(ptr, o, n) \ - _arch_cmpxchg((ptr), (o), (n), "", RISCV_RELEASE_BARRIER, "") + _arch_cmpxchg((ptr), (o), (n), "", ".rl", \ + RISCV_RELEASE_BARRIER, "") #define arch_cmpxchg(ptr, o, n) \ - _arch_cmpxchg((ptr), (o), (n), ".rl", "", " fence rw, rw\n") + _arch_cmpxchg((ptr), (o), (n), ".rl", ".aqrl", \ + "", RISCV_FULL_BARRIER) #define arch_cmpxchg_local(ptr, o, n) \ arch_cmpxchg_relaxed((ptr), (o), (n)) -- 2.39.2