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Re: [libvirt] [PATCH] qemu: don't setup cpuset.mems if memory mode in numatune is 'preferred'

On Wed, Nov 05, 2014 at 12:00:14PM +0800, Wang Rui wrote:
On 2014/11/4 22:04, Martin Kletzander wrote:
On Tue, Nov 04, 2014 at 09:22:22PM +0800, Wang Rui wrote:
If the memory mode is specified as preferred, we get the following error when
starting domain.

error: Unable to write to '$my_cgroup_path/cpuset.mems': Device or resource busy

XML is configured with numatune as follows:
   <memory mode='preferred' nodeset='0'/>

If memory mode is 'preferred', cpuset.mems in cgroup shouldn't be set to
'nodeset'. I find that maybe commit 1a7be8c600905aa07ac2d78293336ba8523ad48e
changes the former logic of checking mode in virDomainNumatuneGetNodeset.

Signed-off-by: Wang Rui <moon wangrui huawei com>
src/qemu/qemu_cgroup.c | 5 +++++
1 file changed, 5 insertions(+)

Thanks for catching that, it definitely is a problem, but I think it
is cause by commit 93e82727ec11d471d2ef3a18835e1fdfe062cef1.

It should be also fixed in virLXCCgroupSetupCpusetTune() for LXC.

OK. I'll try to fix it for LXC in another patch.

Yeah, that can be a follow-up, it'll look the same, anyway.

diff --git a/src/qemu/qemu_cgroup.c b/src/qemu/qemu_cgroup.c
index b5bdb36..8685d6f 100644
--- a/src/qemu/qemu_cgroup.c
+++ b/src/qemu/qemu_cgroup.c
@@ -618,6 +618,11 @@ qemuSetupCpusetMems(virDomainObjPtr vm,
    if (!virCgroupHasController(priv->cgroup, VIR_CGROUP_CONTROLLER_CPUSET))
        return 0;

+    if (virDomainNumatuneGetMode(vm->def->numatune, -1) !=
+        return 0;
+    }

One question, is it problem only for 'preferred' or 'interleaved' as
well?  Because if it's only problem for 'preferred', then the check is
wrong.  If it's problem for 'interleaved' as well, then the commit
message is wrong.

'interleave' with a single node(such as nodeset='0') will cause the same error.
But 'interleave' mode should not live with a single node. So maybe there's
another bugfix to check 'interleave' with single node.

Well, I'd be OK with just changing the commit message to mention that.
This fix is still a valid one and will fix both issues, won't it?

If configured with 'interleave' and multiple nodes(such as nodeset='0-1'),
VM can be started successfully. And cpuset.mems is set to the same nodeset.
So I'll revise my patch.

I'll send patches V2. Conclusion:

1/3 : add check for 'interleave' mode with single numa node
2/3 : fix this problem in qemu
3/3 : fix this problem in lxc

Is it OK?

Anyway, after either one is fixed, I can push this.

Thank you,

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