From patchwork Mon Jul 6 04:35:40 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nicholas Piggin X-Patchwork-Id: 1323323 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=kvm-ppc-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20161025 header.b=XOdg5H2E; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4B0Xp76NrDz9sTw for ; Mon, 6 Jul 2020 14:36:31 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728823AbgGFEg2 (ORCPT ); Mon, 6 Jul 2020 00:36:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49206 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728466AbgGFEg2 (ORCPT ); Mon, 6 Jul 2020 00:36:28 -0400 Received: from mail-wm1-x343.google.com (mail-wm1-x343.google.com [IPv6:2a00:1450:4864:20::343]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2958FC061794; Sun, 5 Jul 2020 21:36:28 -0700 (PDT) Received: by mail-wm1-x343.google.com with SMTP id o8so37800804wmh.4; Sun, 05 Jul 2020 21:36:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=cAuLxDL8CkBp1tpBnhqClilHhcD0O782TDI+bdg1kNU=; b=XOdg5H2E4lNGYFhYc0/rxP9u8/fuTv6VeFja8Noz+koduO9ASBPQiUJIZhJUoe3FZ1 5j6pJEMPoDcUJa4a693ePzR0S0bWCuP+okHF201wWOQJPeFXc19q1Wjad8zvFortsca4 BAU2cWVym6HmdO3WF6QoeaegeTIDsaaabWgHbqVLzx2BEzkwec86jclgPu2E2A4yUupb d2wbC887pQ79Xz0sn+vujqemnZPZJNUPEuhO9Ih5S3OuA12J314AIXAeIrWLtZfjUxBp DPfOl5ls1Z513+Q9hqkmMlLQbBDtAUtP8bHoauVyDliR6Voin8q9hhSW7niY5xE76rE4 BlLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=cAuLxDL8CkBp1tpBnhqClilHhcD0O782TDI+bdg1kNU=; b=bWze14XuD7ETshOYdBvGCLIa1YxkZSVULXH4g0ZPhOoVFVlIIGX2rZNfhxr10gJO+C Yylr+1/UGO4I9yUREDNI0/yJVaF0McGyVAy4zvIg3rJdfOgTVY3EZp+ENe1C0nZtldha mP5I01QsU5r9r1brjioQPfO3/IMcjv2FbyMi1h8l+1y9YCVsTpB7XoFue2O1v1SMy81y tmWPdm6C1b2GhYEqQ+pOjI3syf7VyFwFSIi6h00NgBT1T9WcwvitoV/M1Yzb/ipdA7RQ 99CshD/SmGM0vAC0dBFObX8rWeAVTO39BGM7Ql//pORd0Ca2+VvytOg2TXxuSrSfN8uV 2VlQ== X-Gm-Message-State: AOAM531gYmRqXO1FWa2m6dHABgJJKuc7cxsQNXfTC6osxeADTtsnScd7 LfM9OnQ+9vVeBPCXGPuqoEc= X-Google-Smtp-Source: ABdhPJw3xwCHjl66IDwjNwnrVaS+sYKKRxEjT29tJBVhRnVy0iHX8mmwPpg7n6zCTYEyHFzW18ALwQ== X-Received: by 2002:a7b:c44d:: with SMTP id l13mr49403893wmi.66.1594010186996; Sun, 05 Jul 2020 21:36:26 -0700 (PDT) Received: from bobo.ibm.com (61-68-186-125.tpgi.com.au. [61.68.186.125]) by smtp.gmail.com with ESMTPSA id r10sm22202309wrm.17.2020.07.05.21.36.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 05 Jul 2020 21:36:26 -0700 (PDT) From: Nicholas Piggin To: linuxppc-dev@lists.ozlabs.org Cc: Nicholas Piggin , Will Deacon , Peter Zijlstra , Boqun Feng , Ingo Molnar , Waiman Long , Anton Blanchard , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org Subject: [PATCH v3 6/6] powerpc/qspinlock: optimised atomic_try_cmpxchg_lock that adds the lock hint Date: Mon, 6 Jul 2020 14:35:40 +1000 Message-Id: <20200706043540.1563616-7-npiggin@gmail.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20200706043540.1563616-1-npiggin@gmail.com> References: <20200706043540.1563616-1-npiggin@gmail.com> MIME-Version: 1.0 Sender: kvm-ppc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm-ppc@vger.kernel.org This brings the behaviour of the uncontended fast path back to roughly equivalent to simple spinlocks -- a single atomic op with lock hint. Signed-off-by: Nicholas Piggin --- arch/powerpc/include/asm/atomic.h | 28 ++++++++++++++++++++++++++++ arch/powerpc/include/asm/qspinlock.h | 2 +- 2 files changed, 29 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/atomic.h b/arch/powerpc/include/asm/atomic.h index 498785ffc25f..f6a3d145ffb7 100644 --- a/arch/powerpc/include/asm/atomic.h +++ b/arch/powerpc/include/asm/atomic.h @@ -193,6 +193,34 @@ static __inline__ int atomic_dec_return_relaxed(atomic_t *v) #define atomic_xchg(v, new) (xchg(&((v)->counter), new)) #define atomic_xchg_relaxed(v, new) xchg_relaxed(&((v)->counter), (new)) +/* + * Don't want to override the generic atomic_try_cmpxchg_acquire, because + * we add a lock hint to the lwarx, which may not be wanted for the + * _acquire case (and is not used by the other _acquire variants so it + * would be a surprise). + */ +static __always_inline bool +atomic_try_cmpxchg_lock(atomic_t *v, int *old, int new) +{ + int r, o = *old; + + __asm__ __volatile__ ( +"1:\t" PPC_LWARX(%0,0,%2,1) " # atomic_try_cmpxchg_acquire \n" +" cmpw 0,%0,%3 \n" +" bne- 2f \n" +" stwcx. %4,0,%2 \n" +" bne- 1b \n" +"\t" PPC_ACQUIRE_BARRIER " \n" +"2: \n" + : "=&r" (r), "+m" (v->counter) + : "r" (&v->counter), "r" (o), "r" (new) + : "cr0", "memory"); + + if (unlikely(r != o)) + *old = r; + return likely(r == o); +} + /** * atomic_fetch_add_unless - add unless the number is a given value * @v: pointer of type atomic_t diff --git a/arch/powerpc/include/asm/qspinlock.h b/arch/powerpc/include/asm/qspinlock.h index f5066f00a08c..b752d34517b3 100644 --- a/arch/powerpc/include/asm/qspinlock.h +++ b/arch/powerpc/include/asm/qspinlock.h @@ -37,7 +37,7 @@ static __always_inline void queued_spin_lock(struct qspinlock *lock) { u32 val = 0; - if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL))) + if (likely(atomic_try_cmpxchg_lock(&lock->val, &val, _Q_LOCKED_VAL))) return; queued_spin_lock_slowpath(lock, val);