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Tue, 28 May 2024 11:16:36 -0700 (PDT) Received: from andrea ([151.76.32.59]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a62c501e85dsm394788766b.117.2024.05.28.11.16.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 May 2024 11:16:36 -0700 (PDT) Date: Tue, 28 May 2024 20:16:31 +0200 From: Andrea Parri To: Alexandre Ghiti Cc: Jonathan Corbet , Paul Walmsley , Palmer Dabbelt , Albert Ou , 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 Subject: Re: [PATCH 1/7] riscv: Implement cmpxchg32/64() using Zacas Message-ID: References: <20240528151052.313031-1-alexghiti@rivosinc.com> <20240528151052.313031-2-alexghiti@rivosinc.com> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240528151052.313031-2-alexghiti@rivosinc.com> > + asm goto(ALTERNATIVE("nop", "j %[zacas]", 0, \ > + RISCV_ISA_EXT_ZACAS, 1) \ > + : : : : zacas); \ > + \ > __asm__ __volatile__ ( \ > prepend \ > "0: lr" lr_sfx " %0, %2\n" \ > " bne %0, %z3, 1f\n" \ > - " sc" sc_sfx " %1, %z4, %2\n" \ > + " sc" sc_cas_sfx " %1, %z4, %2\n" \ > " bnez %1, 0b\n" \ > append \ > "1:\n" \ > : "=&r" (r), "=&r" (__rc), "+A" (*(p)) \ > : "rJ" (co o), "rJ" (n) \ > : "memory"); \ > + goto end; \ > + \ > +zacas: \ > + __asm__ __volatile__ ( \ > + prepend \ > + " amocas" sc_cas_sfx " %0, %z2, %1\n" \ > + append \ > + : "+&r" (r), "+A" (*(p)) \ > + : "rJ" (n) \ > + : "memory"); \ With this, a cmpxchg32() will result in something like amocas.w.rl a5,a4,(s1) fence rw,rw (cf. my remarks in patch #4); this will/should provide enough sync, but you might want to try the alternative and currently more common mapping for "fully-ordered AMO sequences", aka amocas.w.aqrl a5,a4,(s1) Similarly for cmpxchg64 and other sizes. 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X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org > + asm goto(ALTERNATIVE("nop", "j %[zacas]", 0, \ > + RISCV_ISA_EXT_ZACAS, 1) \ > + : : : : zacas); \ > + \ > __asm__ __volatile__ ( \ > prepend \ > "0: lr" lr_sfx " %0, %2\n" \ > " bne %0, %z3, 1f\n" \ > - " sc" sc_sfx " %1, %z4, %2\n" \ > + " sc" sc_cas_sfx " %1, %z4, %2\n" \ > " bnez %1, 0b\n" \ > append \ > "1:\n" \ > : "=&r" (r), "=&r" (__rc), "+A" (*(p)) \ > : "rJ" (co o), "rJ" (n) \ > : "memory"); \ > + goto end; \ > + \ > +zacas: \ > + __asm__ __volatile__ ( \ > + prepend \ > + " amocas" sc_cas_sfx " %0, %z2, %1\n" \ > + append \ > + : "+&r" (r), "+A" (*(p)) \ > + : "rJ" (n) \ > + : "memory"); \ With this, a cmpxchg32() will result in something like amocas.w.rl a5,a4,(s1) fence rw,rw (cf. my remarks in patch #4); this will/should provide enough sync, but you might want to try the alternative and currently more common mapping for "fully-ordered AMO sequences", aka amocas.w.aqrl a5,a4,(s1) Similarly for cmpxchg64 and other sizes. Andrea _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv