From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C6969C433F5 for ; Wed, 20 Apr 2022 14:45:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345374AbiDTOr6 (ORCPT ); Wed, 20 Apr 2022 10:47:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46340 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1379768AbiDTOrb (ORCPT ); Wed, 20 Apr 2022 10:47:31 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F357B42A30; Wed, 20 Apr 2022 07:44:44 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 7D94C61647; Wed, 20 Apr 2022 14:44:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A5450C385AC; Wed, 20 Apr 2022 14:44:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1650465883; bh=sAulfPUiEvDbBqRnfY9vU25oXxTZrbt8To4Bji3mwyY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tPXOZu0vrdrkEajEXD7J4RwxL7f29AjfbOT4IBcggA0PvPHAGfMQ2HUqG/l9bNmaU lYhzbIMGzYCYZyrUAfSa2jsWQ3pKmKBZoU2c86KVsBFv1bxaiQMfUMllfUDNQl+xsG O4qH0JQR1ho6ORYR7LbnQVTkRQPGCwSSgiTjotL1aKCdlkZ4gYR+rH8gKX8Y/wN8mP t81UsuPTKux+lMBZU/4NP9QYgY2wdmSUY8OAPZ6Z6lEjYaMKBNCnLMcvGiC/ROX0nk uYkJmZVIDlsyrhaTn6YY/bkOt3Ou5lrsgNlrct74cxs8knSuRN7/2vtmiCHxHPrxaS jnyGB6S4/X81g== From: guoren@kernel.org To: guoren@kernel.org, arnd@arndb.de, palmer@dabbelt.com, mark.rutland@arm.com, will@kernel.org, peterz@infradead.org, boqun.feng@gmail.com, dlustig@nvidia.com, parri.andrea@gmail.com Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Guo Ren Subject: [PATCH V3 3/5] riscv: atomic: Optimize memory barrier semantics of LRSC-pairs Date: Wed, 20 Apr 2022 22:44:15 +0800 Message-Id: <20220420144417.2453958-4-guoren@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220420144417.2453958-1-guoren@kernel.org> References: <20220420144417.2453958-1-guoren@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Guo Ren The current implementation is the same with 8e86f0b409a4 ("arm64: atomics: fix use of acquire + release for full barrier semantics"). RISC-V could combine acquire and release into the AMO instructions and it could reduce the cost of instruction in performance. Here is RISC-V ISA 10.2 Load-Reserved/Store-Conditional Instructions: - .aq: The LR/SC sequence can be given acquire semantics by setting the aq bit on the LR instruction. - .rl: The LR/SC sequence can be given release semantics by setting the rl bit on the SC instruction. - .aqrl: Setting the aq bit on the LR instruction, and setting both the aq and the rl bit on the SC instruction makes the LR/SC sequence sequentially consistent, meaning that it cannot be reordered with earlier or later memory operations from the same hart. Software should not set the rl bit on an LR instruction unless the aq bit is also set, nor should software set the aq bit on an SC instruction unless the rl bit is also set. LR.rl and SC.aq instructions are not guaranteed to provide any stronger ordering than those with both bits clear, but may result in lower performance. Signed-off-by: Guo Ren Signed-off-by: Guo Ren Cc: Palmer Dabbelt Cc: Mark Rutland Cc: Dan Lustig Cc: Andrea Parri --- arch/riscv/include/asm/atomic.h | 6 ++---- arch/riscv/include/asm/cmpxchg.h | 6 ++---- 2 files changed, 4 insertions(+), 8 deletions(-) diff --git a/arch/riscv/include/asm/atomic.h b/arch/riscv/include/asm/atomic.h index 20ce8b83bc18..4aaf5b01e7c6 100644 --- a/arch/riscv/include/asm/atomic.h +++ b/arch/riscv/include/asm/atomic.h @@ -382,9 +382,8 @@ static __always_inline int arch_atomic_sub_if_positive(atomic_t *v, int offset) "0: lr.w %[p], %[c]\n" " sub %[rc], %[p], %[o]\n" " bltz %[rc], 1f\n" - " sc.w.rl %[rc], %[rc], %[c]\n" + " sc.w.aqrl %[rc], %[rc], %[c]\n" " bnez %[rc], 0b\n" - " fence rw, rw\n" "1:\n" : [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter) : [o]"r" (offset) @@ -404,9 +403,8 @@ static __always_inline s64 arch_atomic64_sub_if_positive(atomic64_t *v, s64 offs "0: lr.d %[p], %[c]\n" " sub %[rc], %[p], %[o]\n" " bltz %[rc], 1f\n" - " sc.d.rl %[rc], %[rc], %[c]\n" + " sc.d.aqrl %[rc], %[rc], %[c]\n" " bnez %[rc], 0b\n" - " fence rw, rw\n" "1:\n" : [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter) : [o]"r" (offset) diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h index 1af8db92250b..9269fceb86e0 100644 --- a/arch/riscv/include/asm/cmpxchg.h +++ b/arch/riscv/include/asm/cmpxchg.h @@ -307,9 +307,8 @@ __asm__ __volatile__ ( \ "0: lr.w %0, %2\n" \ " bne %0, %z3, 1f\n" \ - " sc.w.rl %1, %z4, %2\n" \ + " sc.w.aqrl %1, %z4, %2\n" \ " bnez %1, 0b\n" \ - " fence rw, rw\n" \ "1:\n" \ : "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \ : "rJ" ((long)__old), "rJ" (__new) \ @@ -319,9 +318,8 @@ __asm__ __volatile__ ( \ "0: lr.d %0, %2\n" \ " bne %0, %z3, 1f\n" \ - " sc.d.rl %1, %z4, %2\n" \ + " sc.d.aqrl %1, %z4, %2\n" \ " bnez %1, 0b\n" \ - " fence rw, rw\n" \ "1:\n" \ : "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \ : "rJ" (__old), "rJ" (__new) \ -- 2.25.1