From patchwork Thu Nov 19 15:39:15 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 1403098 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=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=cMcK+Gel; dkim-atps=neutral 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 ozlabs.org (Postfix) with ESMTPS id 4CcPD82ylhz9sT6 for ; Fri, 20 Nov 2020 02:46:16 +1100 (AEDT) Received: from localhost ([::1]:38392 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kfm8U-0006J8-BN for incoming@patchwork.ozlabs.org; Thu, 19 Nov 2020 10:46:14 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:42184) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kfm46-0001fJ-W6 for qemu-devel@nongnu.org; Thu, 19 Nov 2020 10:41:43 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26563) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kfm40-00026U-Tz for qemu-devel@nongnu.org; Thu, 19 Nov 2020 10:41:42 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1605800496; 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=qkTlf+6UvOjivvmDtpsBQ03QFDNl9a22E+qx4MkAjVg=; b=cMcK+GelBCUyOomPbkkjY2grszPmQnzBPDdthm2PhAMgSf/+EC5m6twkGxsDVlSeFJuPj/ /opfGFbjmoW8o8nhfIKzDsRbcBxrdp+7vRNCdY2QXnWL0M50r2MDnlcYVAa9KTcSjyuf2L scxc8MXxgmehrZp8CRmIfgNgDpsCv44= 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-460-_YdsxalvPXO49vq-L9M_eA-1; Thu, 19 Nov 2020 10:41:34 -0500 X-MC-Unique: _YdsxalvPXO49vq-L9M_eA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DE04C8AEA44; Thu, 19 Nov 2020 15:41:32 +0000 (UTC) Received: from t480s.redhat.com (ovpn-114-158.ams2.redhat.com [10.36.114.158]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4F4395C1A1; Thu, 19 Nov 2020 15:41:14 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Subject: [PATCH v1 6/9] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require) Date: Thu, 19 Nov 2020 16:39:15 +0100 Message-Id: <20201119153918.120976-7-david@redhat.com> In-Reply-To: <20201119153918.120976-1-david@redhat.com> References: <20201119153918.120976-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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 Received-SPF: pass client-ip=63.128.21.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/18 23:36:20 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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 , Wei Yang , David Hildenbrand , "Michael S. Tsirkin" , "Dr . David Alan Gilbert" , Peter Xu , Luiz Capitulino , Auger Eric , Alex Williamson , teawater , Igor Mammedov , Paolo Bonzini , Marek Kedzierski Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.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 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 Reviewed-by: Peter Xu --- softmmu/physmem.c | 70 ++++++++++++++++++++++++++--------------------- 1 file changed, 39 insertions(+), 31 deletions(-) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index 3027747c03..448e4e8c86 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -3650,56 +3650,64 @@ 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); }