From nobody Mon Feb 9 23:38:35 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1625686904359853.0517168825643; Wed, 7 Jul 2021 12:41:44 -0700 (PDT) Received: from localhost ([::1]:55266 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1m1DQV-0001j3-8z for importer@patchew.org; Wed, 07 Jul 2021 15:41:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45438) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m1DJZ-0004BO-H3 for qemu-devel@nongnu.org; Wed, 07 Jul 2021 15:34:33 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:41024) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m1DJW-0007nv-HU for qemu-devel@nongnu.org; Wed, 07 Jul 2021 15:34:33 -0400 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-505-kQaNX9OPPUKCenRNG8JFYQ-1; Wed, 07 Jul 2021 15:34:28 -0400 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 E0C821023F45; Wed, 7 Jul 2021 19:34:26 +0000 (UTC) Received: from localhost (ovpn-113-79.rdu2.redhat.com [10.10.113.79]) by smtp.corp.redhat.com (Postfix) with ESMTP id B90BD100EBB0; Wed, 7 Jul 2021 19:34:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1625686470; 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=muJDJ7+wfZs2/M1m0FdspOh9UZ+U4wDZmyCZZIiyx5A=; b=RFXgj1NTysGWtxp+oDG2fb1kpPAemvmHf6mAHAoriOqlWT1/9Cmfb6rmnKyYjlaFIHSdA2 BjGuS+zMHpWgsSxIrZwNbWZrYa6u4yis3X5rGBMoFidnzQomViCzP12uZ9jcZ1l95kq5iG bjU2c7UWM9LGuYLEuN2b5McIdIYhdCI= X-MC-Unique: kQaNX9OPPUKCenRNG8JFYQ-1 From: Eduardo Habkost To: Peter Maydell , qemu-devel@nongnu.org Subject: [PULL 12/15] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require) Date: Wed, 7 Jul 2021 15:32:38 -0400 Message-Id: <20210707193241.2659335-13-ehabkost@redhat.com> In-Reply-To: <20210707193241.2659335-1-ehabkost@redhat.com> References: <20210707193241.2659335-1-ehabkost@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=ehabkost@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=216.205.24.124; envelope-from=ehabkost@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.439, 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_H4=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: Pankaj Gupta , Eduardo Habkost , David Hildenbrand , "Michael S . Tsirkin" , Alex Williamson , Peter Xu , "Dr . David Alan Gilbert" , Auger Eric , Pankaj Gupta , teawater , Igor Mammedov , Paolo Bonzini , Marek Kedzierski , Wei Yang Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) X-ZM-MESSAGEID: 1625686905577100003 Content-Type: text/plain; charset="utf-8" From: David Hildenbrand 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 Acked-by: Michael S. Tsirkin 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 Message-Id: <20210413095531.25603-11-david@redhat.com> Signed-off-by: Eduardo Habkost --- softmmu/physmem.c | 70 ++++++++++++++++++++++++++--------------------- 1 file changed, 39 insertions(+), 31 deletions(-) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index 9b171c9dbe5..f1275b61f84 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -3684,56 +3684,64 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, = MemoryRegion *root) } } =20 -/* - * 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_required_cnt; +static unsigned int ram_block_discard_disabled_cnt; +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); +} =20 int ram_block_discard_disable(bool state) { - int old; + int ret =3D 0; =20 + ram_block_discard_disable_mutex_lock(); if (!state) { - qatomic_dec(&ram_block_discard_disabled); - return 0; + ram_block_discard_disabled_cnt--; + } else if (!ram_block_discard_required_cnt) { + ram_block_discard_disabled_cnt++; + } else { + ret =3D -EBUSY; } - - do { - old =3D qatomic_read(&ram_block_discard_disabled); - if (old < 0) { - return -EBUSY; - } - } while (qatomic_cmpxchg(&ram_block_discard_disabled, - old, old + 1) !=3D old); - return 0; + ram_block_discard_disable_mutex_unlock(); + return ret; } =20 int ram_block_discard_require(bool state) { - int old; + int ret =3D 0; =20 + ram_block_discard_disable_mutex_lock(); if (!state) { - qatomic_inc(&ram_block_discard_disabled); - return 0; + ram_block_discard_required_cnt--; + } else if (!ram_block_discard_disabled_cnt) { + ram_block_discard_required_cnt++; + } else { + ret =3D -EBUSY; } - - do { - old =3D qatomic_read(&ram_block_discard_disabled); - if (old > 0) { - return -EBUSY; - } - } while (qatomic_cmpxchg(&ram_block_discard_disabled, - old, old - 1) !=3D old); - return 0; + ram_block_discard_disable_mutex_unlock(); + return ret; } =20 bool ram_block_discard_is_disabled(void) { - return qatomic_read(&ram_block_discard_disabled) > 0; + return qatomic_read(&ram_block_discard_disabled_cnt); } =20 bool ram_block_discard_is_required(void) { - return qatomic_read(&ram_block_discard_disabled) < 0; + return qatomic_read(&ram_block_discard_required_cnt); } --=20 2.31.1