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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4411AC433EF for ; Sat, 9 Oct 2021 10:08:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2789660F94 for ; Sat, 9 Oct 2021 10:08:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244855AbhJIKKB (ORCPT ); Sat, 9 Oct 2021 06:10:01 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:49538 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244657AbhJIKJR (ORCPT ); Sat, 9 Oct 2021 06:09:17 -0400 Date: Sat, 09 Oct 2021 10:07:19 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1633774040; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=g3pCBjl2e8Da4p/V5bnaKUuPbwpFUMahEuvVM8sY/DQ=; b=JWvu76gdJK4gakbpZXUsiXssoLjGVFF68PWDzVDaz+bvWmiIjCu8+/rZIQiwFuIwxSelYH QDxsfEHwOs2HAi+0A9k+V5KlX5dcRjSH5G5JIsrwAkvxh6NninVQOg7LYqa93yNUanmfoq +hOqUxrngflxDDozIV7TvyCLiyVI5ue+cp76hkXI/on+bQlFuKxc9D5BnDIz/LhNlnKMz4 zko9ZhKNpTH2fgwuQrqGUsIGBifR9YyDmlxJwivZWL9JvOR7wUFlo7QovKd0EvpAQniUEm hiHaXYstA3G7yJ2gJVL2npE+acokJ1HOb3x/AbEHsjUPoWJ0yynPNBnidC5T3Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1633774040; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=g3pCBjl2e8Da4p/V5bnaKUuPbwpFUMahEuvVM8sY/DQ=; b=oUt1K8HkA3xxfbv3X0XycH3RojsFD3JBVyND763c59RhE1NYAR9spqB0kdyWQlzdgV23D1 XoaxaLLdS5tarWCQ== From: "tip-bot2 for Davidlohr Bueso" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/core] locking/rwbase: Optimize rwbase_read_trylock Cc: Davidlohr Bueso , "Peter Zijlstra (Intel)" , Waiman Long , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20210920052031.54220-2-dave@stgolabs.net> References: <20210920052031.54220-2-dave@stgolabs.net> MIME-Version: 1.0 Message-ID: <163377403924.25758.18240935726439029694.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the locking/core branch of tip: Commit-ID: c78416d122243c92992a1d1063f17ddd0bc80e6c Gitweb: https://git.kernel.org/tip/c78416d122243c92992a1d1063f17ddd0bc80e6c Author: Davidlohr Bueso AuthorDate: Sun, 19 Sep 2021 22:20:30 -07:00 Committer: Peter Zijlstra CommitterDate: Thu, 07 Oct 2021 13:51:07 +02:00 locking/rwbase: Optimize rwbase_read_trylock Instead of a full barrier around the Rmw insn, micro-optimize for weakly ordered archs such that we only provide the required ACQUIRE semantics when taking the read lock. Signed-off-by: Davidlohr Bueso Signed-off-by: Peter Zijlstra (Intel) Acked-by: Waiman Long Link: https://lkml.kernel.org/r/20210920052031.54220-2-dave@stgolabs.net --- kernel/locking/rwbase_rt.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c index 15c8110..6fd3162 100644 --- a/kernel/locking/rwbase_rt.c +++ b/kernel/locking/rwbase_rt.c @@ -59,8 +59,7 @@ static __always_inline int rwbase_read_trylock(struct rwbase_rt *rwb) * set. */ for (r = atomic_read(&rwb->readers); r < 0;) { - /* Fully-ordered if cmpxchg() succeeds, provides ACQUIRE */ - if (likely(atomic_try_cmpxchg(&rwb->readers, &r, r + 1))) + if (likely(atomic_try_cmpxchg_acquire(&rwb->readers, &r, r + 1))) return 1; } return 0; @@ -187,7 +186,7 @@ static inline void __rwbase_write_unlock(struct rwbase_rt *rwb, int bias, /* * _release() is needed in case that reader is in fast path, pairing - * with atomic_try_cmpxchg() in rwbase_read_trylock(), provides RELEASE + * with atomic_try_cmpxchg_acquire() in rwbase_read_trylock(). */ (void)atomic_add_return_release(READER_BIAS - bias, &rwb->readers); raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);