From nobody Mon Nov 3 20:06:04 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1505995797734815.7888873236697; Thu, 21 Sep 2017 05:09:57 -0700 (PDT) Received: from localhost ([::1]:53383 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dv0Im-0003a6-Uk for importer@patchew.org; Thu, 21 Sep 2017 08:09:57 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39304) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dv0Gv-0002IU-J7 for qemu-devel@nongnu.org; Thu, 21 Sep 2017 08:08:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dv0Gr-00029E-Ue for qemu-devel@nongnu.org; Thu, 21 Sep 2017 08:08:01 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55632) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dv0Gr-00026w-NW for qemu-devel@nongnu.org; Thu, 21 Sep 2017 08:07:57 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CD97B883C3; Thu, 21 Sep 2017 12:07:56 +0000 (UTC) Received: from donizetti.redhat.com (ovpn-117-52.ams2.redhat.com [10.36.117.52]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0E1875EDF9; Thu, 21 Sep 2017 12:07:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com CD97B883C3 Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=pbonzini@redhat.com From: Paolo Bonzini To: qemu-devel@nongnu.org Date: Thu, 21 Sep 2017 14:07:51 +0200 Message-Id: <20170921120751.3027-4-pbonzini@redhat.com> In-Reply-To: <20170921120751.3027-1-pbonzini@redhat.com> References: <20170921120751.3027-1-pbonzini@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Thu, 21 Sep 2017 12:07:56 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH 3/3] memory: Share special empty FlatView X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: aik@ozlabs.ru Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: Alexey Kardashevskiy This shares an cached empty FlatView among address spaces. The empty FV is used every time when a root MR would render into a FV without memory sections, which happens when MR or its children are not enabled (or zero-sized, which isn't caught yet). The empty_view is not NULL to keep the rest of memory API intact; it also has a dispatch tree for the same reason. On POWER8 with 255 CPUs, 255 virtio-net, 40 PCI bridges guest this halves the amount of FlatView's in use (557 -> 260) and dispatch tables (~800000 -> ~370000). In an unrelated experiment with 112 non-virtio devices on x86 ("-M pc"), only 4 FlatViews are alive while the guest runs. Signed-off-by: Alexey Kardashevskiy Message-Id: <20170921085110.25598-16-aik@ozlabs.ru> Signed-off-by: Paolo Bonzini --- memory.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/memory.c b/memory.c index 3207ae55e2..cb369223b1 100644 --- a/memory.c +++ b/memory.c @@ -316,6 +316,7 @@ static void flatview_ref(FlatView *view) static void flatview_unref(FlatView *view) { if (atomic_fetch_dec(&view->ref) =3D=3D 1) { + assert(view->root); call_rcu(view, flatview_destroy, rcu); } } @@ -761,16 +762,19 @@ static MemoryRegion *memory_region_get_flatview_root(= MemoryRegion *mr) } } } + if (found =3D=3D 0) { + return NULL; + } if (next) { mr =3D next; continue; } } =20 - break; + return mr; } =20 - return mr; + return NULL; } =20 /* Render a memory topology into a list of disjoint absolute ranges. */ @@ -962,12 +966,22 @@ static void address_space_update_topology_pass(Addres= sSpace *as, =20 static void flatviews_init(void) { + static FlatView *empty_view; + if (flat_views) { return; } =20 flat_views =3D g_hash_table_new_full(g_direct_hash, g_direct_equal, NU= LL, (GDestroyNotify) flatview_unref); + if (!empty_view) { + empty_view =3D generate_memory_topology(NULL); + /* We keep it alive forever in the global variable. */ + flatview_ref(empty_view); + } else { + g_hash_table_replace(flat_views, NULL, empty_view); + flatview_ref(empty_view); + } } =20 static void flatviews_reset(void) --=20 2.13.5