From ac89574e251dfecf34606083e402194ded63dba2 Mon Sep 17 00:00:00 2001 Message-Id: From: Michal Privoznik Date: Wed, 5 Jun 2019 11:33:29 +0200 Subject: [PATCH] qemu: Set up EMULATOR thread and cpuset.mems before exec()-ing qemu It's funny how this went unnoticed for such a long time. Long story short, if a domain is configured with VIR_DOMAIN_NUMATUNE_MEM_STRICT libvirt doesn't really honour that. This is because of 7e72ac787848 after which libvirt allowed qemu to allocate memory just anywhere and only after that it used some magic involving cpuset.memory_migrate and cpuset.mems to move the memory to desired NUMA nodes. This was done in order to work around some KVM bug where KVM would fail if there wasn't a DMA zone available on the NUMA node. Well, while the work around might stopped libvirt tickling the KVM bug it also caused a bug on libvirt side: if there is not enough memory on configured NUMA node(s) then any attempt to start a domain must fail. Because of the way we play with guest memory domains can start just happily. The solution is to move the child we've just forked into emulator cgroup, set up cpuset.mems and exec() qemu only after that. This basically reverts 7e72ac787848b7434c9 which was a workaround for kernel bug. This bug was apparently fixed because I've tested this successfully with recent kernel. Signed-off-by: Michal Privoznik Reviewed-by: Martin Kletzander (cherry picked from commit 0eaa4716e1b8f6eb59d77049aed3735c3b5fbdd6) https://bugzilla.redhat.com/show_bug.cgi?id=1716943 Signed-off-by: Michal Privoznik Message-Id: Reviewed-by: Andrea Bolognani --- src/qemu/qemu_process.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c index 6071b3ba3d..8b05cef80c 100644 --- a/src/qemu/qemu_process.c +++ b/src/qemu/qemu_process.c @@ -6442,6 +6442,10 @@ qemuProcessLaunch(virConnectPtr conn, if (qemuProcessInitCpuAffinity(vm) < 0) goto cleanup; + VIR_DEBUG("Setting emulator tuning/settings"); + if (qemuProcessSetupEmulator(vm) < 0) + goto cleanup; + VIR_DEBUG("Setting cgroup for external devices (if required)"); if (qemuSetupCgroupForExtDevices(vm, driver) < 0) goto cleanup; @@ -6533,10 +6537,6 @@ qemuProcessLaunch(virConnectPtr conn, if (qemuProcessDetectIOThreadPIDs(driver, vm, asyncJob) < 0) goto cleanup; - VIR_DEBUG("Setting emulator tuning/settings"); - if (qemuProcessSetupEmulator(vm) < 0) - goto cleanup; - VIR_DEBUG("Setting global CPU cgroup (if required)"); if (qemuSetupGlobalCpuCgroup(vm) < 0) goto cleanup; -- 2.22.0