From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:42309) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h1ZRE-00059Z-So for qemu-devel@nongnu.org; Wed, 06 Mar 2019 11:30:37 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h1ZR8-00022T-7S for qemu-devel@nongnu.org; Wed, 06 Mar 2019 11:30:32 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47442) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1h1ZR6-0001yu-EG for qemu-devel@nongnu.org; Wed, 06 Mar 2019 11:30:29 -0500 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 mx1.redhat.com (Postfix) with ESMTPS id 1E7083003097 for ; Wed, 6 Mar 2019 16:30:26 +0000 (UTC) From: Igor Mammedov Date: Wed, 6 Mar 2019 17:30:25 +0100 Message-Id: <1551889825-227155-1-git-send-email-imammedo@redhat.com> Subject: [Qemu-devel] [PATCH] numa: warn if numa 'mem' option or default RAM splitting between nodes is used. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: ehabkost@redhat.com, libvir-list@redhat.com, berrange@redhat.com, eblake@redhat.com Ammend -numa option docs and print warnings if 'mem' option or default RAM splitting between nodes is used. It's intended to discourage users from using configuration that allows only to fake NUMA on guest side while leading to reduced performance of the guest due to inability to properly configure VM's RAM on the host. In NUMA case, it's recommended to always explicitly configure guest RAM using -numa node,memdev={backend-id} option. Signed-off-by: Igor Mammedov --- numa.c | 5 +++++ qemu-options.hx | 12 ++++++++---- 2 files changed, 13 insertions(+), 4 deletions(-) diff --git a/numa.c b/numa.c index 3875e1e..c6c2a6f 100644 --- a/numa.c +++ b/numa.c @@ -121,6 +121,8 @@ static void parse_numa_node(MachineState *ms, NumaNodeOptions *node, if (node->has_mem) { numa_info[nodenr].node_mem = node->mem; + warn_report("Parameter -numa node,mem is obsolete," + " use -numa node,memdev instead"); } if (node->has_memdev) { Object *o; @@ -407,6 +409,9 @@ void numa_complete_configuration(MachineState *ms) if (i == nb_numa_nodes) { assert(mc->numa_auto_assign_ram); mc->numa_auto_assign_ram(mc, numa_info, nb_numa_nodes, ram_size); + warn_report("Default splitting of RAM between nodes is obsolete," + " Use '-numa node,memdev' to explictly define RAM" + " allocation per node"); } numa_total = 0; diff --git a/qemu-options.hx b/qemu-options.hx index 1cf9aac..033e311 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -206,10 +206,14 @@ For example: -numa cpu,node-id=0,socket-id=0 -numa cpu,node-id=1,socket-id=1 @end example -@samp{mem} assigns a given RAM amount to a node. @samp{memdev} -assigns RAM from a given memory backend device to a node. If -@samp{mem} and @samp{memdev} are omitted in all nodes, RAM is -split equally between them. +@samp{memdev} assigns RAM from a given memory backend device to a node. + +Legacy options/behaviour: @samp{mem} assigns a given RAM amount to a node. +If @samp{mem} and @samp{memdev} are omitted in all nodes, RAM is split equally +between them. Option @samp{mem} and default RAM splitting are obsolete as they +do not provide means to manage RAM on host side and only allow QEMU to fake +NUMA support which in practice could degrade VM performance. +It's advised to always explicitly configure NUMA RAM using @samp{memdev} option. @samp{mem} and @samp{memdev} are mutually exclusive. Furthermore, if one node uses @samp{memdev}, all of them have to use it. -- 2.7.4