From cdf80365205ad2b05519049eaa9a71c7804bd240 Mon Sep 17 00:00:00 2001 From: Igor Mammedov Date: Thu, 30 May 2019 10:33:18 +0200 Subject: [PATCH] numa: deprecate 'mem' parameter of '-numa node' option The parameter allows to configure fake NUMA topology where guest VM simulates NUMA topology but not actually getting performance benefits from it. The same or better results could be achieved using 'memdev' parameter. Beside of unpredictable performance, '-numa node.mem' option has other issues when it's used with combination of -mem-path + + -mem-prealloc + memdev backends (pc-dimm), breaking binding of memdev backends since mem-path/mem-prealloc are global and affect the most of RAM allocations. It's possible to make memdevs and global -mem-path/mem-prealloc to play nicely together but that will just complicate already complicated code and add unobious ways it could break on 2 different memmory allocation pathes and their combinations. Instead of it, consolidate all guest RAM allocation over memdev which still allows to create fake NUMA configurations if desired and leaves one simplifyed code path to consider when it comes to guest RAM allocation. To achieve desired simplification deprecate 'mem' parameter as its ad-hoc partitioning of initial RAM MemoryRegion can't be translated to memdev based backend transparently to users and in compatible manner (migration wise). Later down the road that will allow to consolidate means of how guest RAM is allocated and would permit us to clean up quite a bit memory allocations and numa code, leaving only 'memdev' implementation in place. Signed-off-by: Igor Mammedov Message-Id: <1559205199-233510-3-git-send-email-imammedo@redhat.com> Signed-off-by: Eduardo Habkost --- hw/core/numa.c | 2 ++ qemu-deprecated.texi | 16 ++++++++++++++++ 2 files changed, 18 insertions(+) diff --git a/hw/core/numa.c b/hw/core/numa.c index 4252af7100..b9e79b8c8b 100644 --- a/hw/core/numa.c +++ b/hw/core/numa.c @@ -118,6 +118,8 @@ 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 deprecated," + " use -numa node,memdev instead"); } if (node->has_memdev) { Object *o; diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi index 40c017b426..ba52999f7f 100644 --- a/qemu-deprecated.texi +++ b/qemu-deprecated.texi @@ -88,6 +88,22 @@ The @code{-realtime mlock=on|off} argument has been replaced by the The ``-virtfs_synth'' argument is now deprecated. Please use ``-fsdev synth'' and ``-device virtio-9p-...'' instead. +@subsection -numa node,mem=@var{size} (since 4.1) + +The parameter @option{mem} of @option{-numa node} is used to assign a part of +guest RAM to a NUMA node. But when using it, it's impossible to manage specified +RAM chunk on the host side (like bind it to a host node, setting bind policy, ...), +so guest end-ups with the fake NUMA configuration with suboptiomal performance. +However since 2014 there is an alternative way to assign RAM to a NUMA node +using parameter @option{memdev}, which does the same as @option{mem} and adds +means to actualy manage node RAM on the host side. Use parameter @option{memdev} +with @var{memory-backend-ram} backend as an replacement for parameter @option{mem} +to achieve the same fake NUMA effect or a properly configured +@var{memory-backend-file} backend to actually benefit from NUMA configuration. +In future new machine versions will not accept the option but it will still +work with old machine types. User can check QAPI schema to see if the legacy +option is supported by looking at MachineInfo::numa-mem-supported property. + @section QEMU Machine Protocol (QMP) commands @subsection block-dirty-bitmap-add "autoload" parameter (since 2.12.0) -- 2.39.2