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=-13.5 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 37EF9C433ED for ; Tue, 13 Apr 2021 10:02:45 +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 C44FE61370 for ; Tue, 13 Apr 2021 10:02:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C44FE61370 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]:40084 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lWFsZ-0004eK-Q2 for qemu-devel@archiver.kernel.org; Tue, 13 Apr 2021 06:02:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41484) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lWFpL-0000tf-CX for qemu-devel@nongnu.org; Tue, 13 Apr 2021 05:59:23 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:53399) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lWFpI-0005S6-17 for qemu-devel@nongnu.org; Tue, 13 Apr 2021 05:59:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618307957; 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=oT3YapBW4mzPMORsz7SDVTLDP4PZpFbsq/Hdc4/fMP8=; b=AFawz1Z/71nYt6OuBZOn6qgihxm2nzdZ6OJ5SXkOFA0agY9daGj8Ug8N5vQoXkM/OzWyb/ XiEp5bb5yNTufUQUujRdK7K4A2DkA9mqr1YuUj9oV9pMHGnp33M1N/eROYPgV96DldBY11 C2Q48mlY7RJeTJKC7GG87vMgT01vfW8= 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-98-CxHDTBjYOIixXjyJFn--Jg-1; Tue, 13 Apr 2021 05:59:15 -0400 X-MC-Unique: CxHDTBjYOIixXjyJFn--Jg-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 D1664107ACCA; Tue, 13 Apr 2021 09:59:14 +0000 (UTC) Received: from t480s.redhat.com (ovpn-115-69.ams2.redhat.com [10.36.115.69]) by smtp.corp.redhat.com (Postfix) with ESMTP id A923B5E1A4; Tue, 13 Apr 2021 09:59:01 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Subject: [PATCH RESEND v7 10/13] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require) Date: Tue, 13 Apr 2021 11:55:28 +0200 Message-Id: <20210413095531.25603-11-david@redhat.com> In-Reply-To: <20210413095531.25603-1-david@redhat.com> References: <20210413095531.25603-1-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 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII" Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_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 , Wei Yang , "Michael S . Tsirkin" , David Hildenbrand , Alex Williamson , Peter Xu , "Dr . David Alan Gilbert" , Auger Eric , Pankaj Gupta , teawater , Igor Mammedov , Paolo Bonzini , Marek Kedzierski 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 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 --- softmmu/physmem.c | 70 ++++++++++++++++++++++++++--------------------- 1 file changed, 39 insertions(+), 31 deletions(-) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index 85034d9c11..aaa2b2eb92 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -3647,56 +3647,64 @@ 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_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); +} 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_disabled_cnt--; + } else if (!ram_block_discard_required_cnt) { + ram_block_discard_disabled_cnt++; + } 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_required_cnt--; + } else if (!ram_block_discard_disabled_cnt) { + ram_block_discard_required_cnt++; + } 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_disabled_cnt); } bool ram_block_discard_is_required(void) { - return qatomic_read(&ram_block_discard_disabled) < 0; + return qatomic_read(&ram_block_discard_required_cnt); } -- 2.30.2