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 X-Spam-Level: X-Spam-Status: No, score=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B42EEC433DB for ; Thu, 21 Jan 2021 11:14:52 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2033723877 for ; Thu, 21 Jan 2021 11:14:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2033723877 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:56322 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l2XvP-0000Xl-54 for qemu-devel@archiver.kernel.org; Thu, 21 Jan 2021 06:14:51 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:47402) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l2XoI-0007Oo-44 for qemu-devel@nongnu.org; Thu, 21 Jan 2021 06:07:30 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:32684) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l2XoG-00071C-1R for qemu-devel@nongnu.org; Thu, 21 Jan 2021 06:07:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611227247; h=from:from: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=DioFTJxae4TxGq/+SrUIxu2PVNai1+MvfFiTLRR/ins=; b=WkCOuRlJUwzwEnRN736GVzZ2CLOcoWjXrdFyvgbxwbpq+I7BdVAUCiIjmRa1zMz5GrsRq8 OtF6GbdMfsShTGs9vqvFR/JHJFUZZAOEHsdLU2kwEhEILvhI3kehI103MMmcoiJAO5MrbK AWlpcXcEJCUtooitfMpS66+hzZOdVX0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-61-FnqbhE1GNLOOWE0Wt_Zlrg-1; Thu, 21 Jan 2021 06:07:23 -0500 X-MC-Unique: FnqbhE1GNLOOWE0Wt_Zlrg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 483301800D41; Thu, 21 Jan 2021 11:07:22 +0000 (UTC) Received: from t480s.redhat.com (ovpn-115-70.ams2.redhat.com [10.36.115.70]) by smtp.corp.redhat.com (Postfix) with ESMTP id 80F1210013BD; Thu, 21 Jan 2021 11:07:16 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Subject: [PATCH v5 08/11] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require) Date: Thu, 21 Jan 2021 12:05:37 +0100 Message-Id: <20210121110540.33704-9-david@redhat.com> In-Reply-To: <20210121110540.33704-1-david@redhat.com> References: <20210121110540.33704-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII" Received-SPF: pass client-ip=216.205.24.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.167, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Marek Kedzierski , Pankaj Gupta , Wei Yang , David Hildenbrand , "Michael S. Tsirkin" , Alex Williamson , Peter Xu , "Dr . David Alan Gilbert" , Auger Eric , Pankaj Gupta , teawater , Jonathan Cameron , Paolo Bonzini , Igor Mammedov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" We have users in migration context that don't hold the BQL (when finishing migration). To prepare for further changes, use a dedicated mutex instead of atomic operations. Keep using qatomic_read ("READ_ONCE") for the functions that only extract the current state (e.g., used by virtio-balloon), locking isn't necessary. While at it, split up the counter into two variables to make it easier to understand. Suggested-by: Peter Xu Reviewed-by: Peter Xu Reviewed-by: Pankaj Gupta Cc: Paolo Bonzini Cc: "Michael S. Tsirkin" Cc: Alex Williamson Cc: Dr. David Alan Gilbert Cc: Igor Mammedov Cc: Pankaj Gupta Cc: Peter Xu Cc: Auger Eric Cc: Wei Yang Cc: teawater Cc: Marek Kedzierski Signed-off-by: David Hildenbrand --- softmmu/physmem.c | 70 ++++++++++++++++++++++++++--------------------- 1 file changed, 39 insertions(+), 31 deletions(-) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index 6301f4f0a5..2e253b8547 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -3660,56 +3660,64 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, MemoryRegion *root) } } -/* - * If positive, discarding RAM is disabled. If negative, discarding RAM is - * required to work and cannot be disabled. - */ -static int ram_block_discard_disabled; +static unsigned int ram_block_discard_requirers; +static unsigned int ram_block_discard_disablers; +static QemuMutex ram_block_discard_disable_mutex; + +static void ram_block_discard_disable_mutex_lock(void) +{ + static gsize initialized; + + if (g_once_init_enter(&initialized)) { + qemu_mutex_init(&ram_block_discard_disable_mutex); + g_once_init_leave(&initialized, 1); + } + qemu_mutex_lock(&ram_block_discard_disable_mutex); +} + +static void ram_block_discard_disable_mutex_unlock(void) +{ + qemu_mutex_unlock(&ram_block_discard_disable_mutex); +} int ram_block_discard_disable(bool state) { - int old; + int ret = 0; + ram_block_discard_disable_mutex_lock(); if (!state) { - qatomic_dec(&ram_block_discard_disabled); - return 0; + ram_block_discard_disablers--; + } else if (!ram_block_discard_requirers) { + ram_block_discard_disablers++; + } else { + ret = -EBUSY; } - - do { - old = qatomic_read(&ram_block_discard_disabled); - if (old < 0) { - return -EBUSY; - } - } while (qatomic_cmpxchg(&ram_block_discard_disabled, - old, old + 1) != old); - return 0; + ram_block_discard_disable_mutex_unlock(); + return ret; } int ram_block_discard_require(bool state) { - int old; + int ret = 0; + ram_block_discard_disable_mutex_lock(); if (!state) { - qatomic_inc(&ram_block_discard_disabled); - return 0; + ram_block_discard_requirers--; + } else if (!ram_block_discard_disablers) { + ram_block_discard_requirers++; + } else { + ret = -EBUSY; } - - do { - old = qatomic_read(&ram_block_discard_disabled); - if (old > 0) { - return -EBUSY; - } - } while (qatomic_cmpxchg(&ram_block_discard_disabled, - old, old - 1) != old); - return 0; + ram_block_discard_disable_mutex_unlock(); + return ret; } bool ram_block_discard_is_disabled(void) { - return qatomic_read(&ram_block_discard_disabled) > 0; + return qatomic_read(&ram_block_discard_disablers); } bool ram_block_discard_is_required(void) { - return qatomic_read(&ram_block_discard_disabled) < 0; + return qatomic_read(&ram_block_discard_requirers); } -- 2.29.2