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 5CAA3C00140 for ; Mon, 8 Aug 2022 07:14:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235543AbiHHHOW (ORCPT ); Mon, 8 Aug 2022 03:14:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55198 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233982AbiHHHOE (ORCPT ); Mon, 8 Aug 2022 03:14:04 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B59909FC0; Mon, 8 Aug 2022 00:14:03 -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 ams.source.kernel.org (Postfix) with ESMTPS id 55D57B80E07; Mon, 8 Aug 2022 07:14:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 13FA8C433D6; Mon, 8 Aug 2022 07:13:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1659942841; bh=VTgzxT5YWA/FXTGh2L0uPc4Dz3cqTkrreO/CY7INghE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bfPqsa8VFloG1NRbhC8enTrVw0OkRGrGcLm+//WoDzQ9TvOTVF75xkB/W5QkB21ty X/CwZ9TYEc/E66B3wvCUHwWY38osrkJhBa/VQjO8x8sCm17Xq3EXus/jyOwRI6q6pl 0i9vN7To7knSIEXDvUSRmzNFJUIT0B6XB9bx2kHRiTc4JjieQpAdn3tUdFr+36K4Li rV+PiNTwZ4E92wpAs5/tCcoRlJxu2vsxg9POGgIdKFPWqnm6QV5+GLcbA5mB4Hy4u3 Y5xrgmB+hTFWRBsHoMNL+WpL4OBjFpR1yVnxV97fa+YUnvw9jhQFzFECEajyBhu4sp QRNjxJEU9Brlw== From: guoren@kernel.org To: palmer@rivosinc.com, heiko@sntech.de, hch@infradead.org, arnd@arndb.de, peterz@infradead.org, will@kernel.org, boqun.feng@gmail.com, longman@redhat.com, shorne@gmail.com, conor.dooley@microchip.com Cc: linux-csky@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Guo Ren , Guo Ren Subject: [PATCH V9 04/15] asm-generic: ticket-lock: Keep ticket-lock the same semantic with qspinlock Date: Mon, 8 Aug 2022 03:13:07 -0400 Message-Id: <20220808071318.3335746-5-guoren@kernel.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220808071318.3335746-1-guoren@kernel.org> References: <20220808071318.3335746-1-guoren@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org From: Guo Ren Define smp_mb__after_spinlock by smp_mb as default behavior to give RCsc synchronization point for all architectures. Keep the same semantic with qspinlock, a acquire (RCpc) synchronization point. More detail, see include/linux/spinlock.h. Some architectures could give more robust semantics than smp_mb, eg. riscv. Some architectures needn't smp_mb__after_spinlock because their spinlocks have contained an RCsc. Signed-off-by: Guo Ren Signed-off-by: Guo Ren Cc: Peter Zijlstra --- include/asm-generic/spinlock.h | 5 +++++ include/asm-generic/ticket_spinlock.h | 18 ++++-------------- 2 files changed, 9 insertions(+), 14 deletions(-) diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h index 970590baf61b..6f5a1b838ca2 100644 --- a/include/asm-generic/spinlock.h +++ b/include/asm-generic/spinlock.h @@ -6,4 +6,9 @@ #include #include +/* See include/linux/spinlock.h */ +#ifndef smp_mb__after_spinlock +#define smp_mb__after_spinlock() smp_mb() +#endif + #endif /* __ASM_GENERIC_SPINLOCK_H */ diff --git a/include/asm-generic/ticket_spinlock.h b/include/asm-generic/ticket_spinlock.h index cfcff22b37b3..d8e6ec82f096 100644 --- a/include/asm-generic/ticket_spinlock.h +++ b/include/asm-generic/ticket_spinlock.h @@ -14,9 +14,8 @@ * a test-and-set. * * It further assumes atomic_*_release() + atomic_*_acquire() is RCpc and hence - * uses atomic_fetch_add() which is RCsc to create an RCsc hot path, along with - * a full fence after the spin to upgrade the otherwise-RCpc - * atomic_cond_read_acquire(). + * uses smp_mb__after_spinlock which is RCsc to create an RCsc hot path, See + * include/linux/spinlock.h * * The implementation uses smp_cond_load_acquire() to spin, so if the * architecture has WFE like instructions to sleep instead of poll for word @@ -32,22 +31,13 @@ static __always_inline void ticket_spin_lock(arch_spinlock_t *lock) { - u32 val = atomic_fetch_add(1<<16, &lock->val); + u32 val = atomic_fetch_add_acquire(1<<16, &lock->val); u16 ticket = val >> 16; if (ticket == (u16)val) return; - /* - * atomic_cond_read_acquire() is RCpc, but rather than defining a - * custom cond_read_rcsc() here we just emit a full fence. We only - * need the prior reads before subsequent writes ordering from - * smb_mb(), but as atomic_cond_read_acquire() just emits reads and we - * have no outstanding writes due to the atomic_fetch_add() the extra - * orderings are free. - */ atomic_cond_read_acquire(&lock->val, ticket == (u16)VAL); - smp_mb(); } static __always_inline bool ticket_spin_trylock(arch_spinlock_t *lock) @@ -57,7 +47,7 @@ static __always_inline bool ticket_spin_trylock(arch_spinlock_t *lock) if ((old >> 16) != (old & 0xffff)) return false; - return atomic_try_cmpxchg(&lock->val, &old, old + (1<<16)); /* SC, for RCsc */ + return atomic_try_cmpxchg_acquire(&lock->val, &old, old + (1<<16)); } static __always_inline void ticket_spin_unlock(arch_spinlock_t *lock) -- 2.36.1