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 ADB49C433F5 for ; Sun, 24 Apr 2022 07:29:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238510AbiDXHcw (ORCPT ); Sun, 24 Apr 2022 03:32:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34376 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238480AbiDXHco (ORCPT ); Sun, 24 Apr 2022 03:32:44 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 937EA151868; Sun, 24 Apr 2022 00:29:44 -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 F21E9612FF; Sun, 24 Apr 2022 07:29:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F2AFC385B1; Sun, 24 Apr 2022 07:29:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1650785383; bh=rk4+4zbLu6epppwE4WRbBhd3KaAhjfLplCUb8DsR/0c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=maI4dy3txuTIlTp12VhWrkJqf4Q2kXf50o6qzRDipwCRtRxdMi5EGsLqmLXGNWxSe DRwL1uqb+YDJJMsRfjHp1/wwSVzfme+sij4aaFWWgKtBCQyuZ4PZTCbJkv8sErUVBe zUD68Co8XO3b2J8Jbcp8kVYdX8BI79hcYIO0lGlctfuYZsiZEaJQ9YUh+RgZWadVo4 CIauvWLbcafUpqoD9G+Jm4n+rBmEqGVVsVxOqwmLdjRtjdHIWggj40/wFjmgt2gWBy r6khlE2b+CkXPnJd9yW+sGlNkwfGz1UNpU8KDUoCaek+n/Uk9h9qx1RzoxYdrqt3yD m495G7bFCk8ww== From: guoren@kernel.org To: guoren@kernel.org, arnd@arndb.de, mark.rutland@arm.com, boqun.feng@gmail.com, peterz@infradead.org, will@kernel.org Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-csky@vger.kernel.org, Guo Ren Subject: [PATCH V4 1/3] csky: atomic: Optimize cmpxchg with acquire & release Date: Sun, 24 Apr 2022 15:29:16 +0800 Message-Id: <20220424072918.2596899-2-guoren@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220424072918.2596899-1-guoren@kernel.org> References: <20220424072918.2596899-1-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 Optimize cmpxchg with ASM acquire/release fence ASM instructions instead of previous generic based. Prevent a fence when cmxchg's first load != old. Comments by Rutland: 8e86f0b409a4 ("arm64: atomics: fix use of acquire + release for full barrier semantics") Comments by Boqun: FWIW, you probably need to make sure that a barrier instruction inside an lr/sc loop is a good thing. IIUC, the execution time of a barrier instruction is determined by the status of store buffers and invalidate queues (and probably other stuffs), so it may increase the execution time of the lr/sc loop, and make it unlikely to succeed. But this really depends on how the arch executes these instructions. Link: https://lore.kernel.org/linux-riscv/CAJF2gTSAxpAi=LbAdu7jntZRUa=-dJwL0VfmDfBV5MHB=rcZ-w@mail.gmail.com/T/#m27a0f1342995deae49ce1d0e1f2683f8a181d6c3 Signed-off-by: Guo Ren Signed-off-by: Guo Ren Cc: Mark Rutland --- arch/csky/include/asm/barrier.h | 11 +++--- arch/csky/include/asm/cmpxchg.h | 64 ++++++++++++++++++++++++++++++--- 2 files changed, 67 insertions(+), 8 deletions(-) diff --git a/arch/csky/include/asm/barrier.h b/arch/csky/include/asm/barrier.h index f4045dd53e17..15de58b10aec 100644 --- a/arch/csky/include/asm/barrier.h +++ b/arch/csky/include/asm/barrier.h @@ -37,17 +37,21 @@ * bar.brar * bar.bwaw */ +#define FULL_FENCE ".long 0x842fc000\n" +#define ACQUIRE_FENCE ".long 0x8427c000\n" +#define RELEASE_FENCE ".long 0x842ec000\n" + #define __bar_brw() asm volatile (".long 0x842cc000\n":::"memory") #define __bar_br() asm volatile (".long 0x8424c000\n":::"memory") #define __bar_bw() asm volatile (".long 0x8428c000\n":::"memory") #define __bar_arw() asm volatile (".long 0x8423c000\n":::"memory") #define __bar_ar() asm volatile (".long 0x8421c000\n":::"memory") #define __bar_aw() asm volatile (".long 0x8422c000\n":::"memory") -#define __bar_brwarw() asm volatile (".long 0x842fc000\n":::"memory") -#define __bar_brarw() asm volatile (".long 0x8427c000\n":::"memory") +#define __bar_brwarw() asm volatile (FULL_FENCE:::"memory") +#define __bar_brarw() asm volatile (ACQUIRE_FENCE:::"memory") #define __bar_bwarw() asm volatile (".long 0x842bc000\n":::"memory") #define __bar_brwar() asm volatile (".long 0x842dc000\n":::"memory") -#define __bar_brwaw() asm volatile (".long 0x842ec000\n":::"memory") +#define __bar_brwaw() asm volatile (RELEASE_FENCE:::"memory") #define __bar_brar() asm volatile (".long 0x8425c000\n":::"memory") #define __bar_brar() asm volatile (".long 0x8425c000\n":::"memory") #define __bar_bwaw() asm volatile (".long 0x842ac000\n":::"memory") @@ -56,7 +60,6 @@ #define __smp_rmb() __bar_brar() #define __smp_wmb() __bar_bwaw() -#define ACQUIRE_FENCE ".long 0x8427c000\n" #define __smp_acquire_fence() __bar_brarw() #define __smp_release_fence() __bar_brwaw() diff --git a/arch/csky/include/asm/cmpxchg.h b/arch/csky/include/asm/cmpxchg.h index d1bef11f8dc9..5b8faccd65e4 100644 --- a/arch/csky/include/asm/cmpxchg.h +++ b/arch/csky/include/asm/cmpxchg.h @@ -64,15 +64,71 @@ extern void __bad_xchg(void); #define arch_cmpxchg_relaxed(ptr, o, n) \ (__cmpxchg_relaxed((ptr), (o), (n), sizeof(*(ptr)))) -#define arch_cmpxchg(ptr, o, n) \ +#define __cmpxchg_acquire(ptr, old, new, size) \ ({ \ + __typeof__(ptr) __ptr = (ptr); \ + __typeof__(new) __new = (new); \ + __typeof__(new) __tmp; \ + __typeof__(old) __old = (old); \ + __typeof__(*(ptr)) __ret; \ + switch (size) { \ + case 4: \ + asm volatile ( \ + "1: ldex.w %0, (%3) \n" \ + " cmpne %0, %4 \n" \ + " bt 2f \n" \ + " mov %1, %2 \n" \ + " stex.w %1, (%3) \n" \ + " bez %1, 1b \n" \ + ACQUIRE_FENCE \ + "2: \n" \ + : "=&r" (__ret), "=&r" (__tmp) \ + : "r" (__new), "r"(__ptr), "r"(__old) \ + :); \ + break; \ + default: \ + __bad_xchg(); \ + } \ + __ret; \ +}) + +#define arch_cmpxchg_acquire(ptr, o, n) \ + (__cmpxchg_acquire((ptr), (o), (n), sizeof(*(ptr)))) + +#define __cmpxchg(ptr, old, new, size) \ +({ \ + __typeof__(ptr) __ptr = (ptr); \ + __typeof__(new) __new = (new); \ + __typeof__(new) __tmp; \ + __typeof__(old) __old = (old); \ __typeof__(*(ptr)) __ret; \ - __smp_release_fence(); \ - __ret = arch_cmpxchg_relaxed(ptr, o, n); \ - __smp_acquire_fence(); \ + switch (size) { \ + case 4: \ + asm volatile ( \ + RELEASE_FENCE \ + "1: ldex.w %0, (%3) \n" \ + " cmpne %0, %4 \n" \ + " bt 2f \n" \ + " mov %1, %2 \n" \ + " stex.w %1, (%3) \n" \ + " bez %1, 1b \n" \ + FULL_FENCE \ + "2: \n" \ + : "=&r" (__ret), "=&r" (__tmp) \ + : "r" (__new), "r"(__ptr), "r"(__old) \ + :); \ + break; \ + default: \ + __bad_xchg(); \ + } \ __ret; \ }) +#define arch_cmpxchg(ptr, o, n) \ + (__cmpxchg((ptr), (o), (n), sizeof(*(ptr)))) + +#define arch_cmpxchg_local(ptr, o, n) \ + (__cmpxchg_relaxed((ptr), (o), (n), sizeof(*(ptr)))) #else #include #endif -- 2.25.1