Re: [Qemu-devel] [PATCH v2 for-2.3] numa: pc: fix default VCPU to node mapping

[Andreas Färber]

Igor,

Some minor nits I overlooked:

Am 18.03.2015 um 17:38 schrieb Igor Mammedov:
> since commit

"Since" :)

>    dd0247e0 pc: acpi: mark all possible CPUs as enabled in SRAT
> Linux kernel actually tries to use CPU to Node mapping from
> QEMU provided SRAT table instead of discarding it, and that
> in some cases breaks build_sched_domains() which expects
> sane mapping where cores/threads belonging to the same socket
> are on the same NUMA node.
> 
> With current default round-robin mapping of VCPUs to nodes
> guest ends-up with cores/threads belonging to the same socket
> being on different NUMA nodes.
> 
> For example with following CLI:
> qemu-kvm -m 4G -smp 5,sockets=2,cores=4,threads=1,maxcpus=8 \
>          -numa node,nodeid=0 -numa node,nodeid=1

There is no qemu-kvm upstream, use qemu-system-x86_64 instead?

Isn't the 5 wrong here? I would expect sockets, cores and threads
overriding that value to 8.

> 2.6.32 based kernels will hang on boot due to incorrectly build

"built"?

> sched_group-s list in update_sd_lb_stats()
> so comment in QEMU justifying dumb default mapping:
>  "
>   guest OSes must cope with this anyway, because there are BIOSes
>   out there in real machines which also use this scheme.
>  "
> isn't really valid.
> 
> Replacing default mapping with a manual, where VCPUs belonging to
> the same socket are on the same NUMA node, fixes issue for

"fixes the issue"

> guests which can't handle nonsense topology i.e. changing CLI to:
>   -numa node,nodeid=0,cpus=0-3 -numa node,nodeid=1,cpus=4-7
> 
> So instead of simply scattering VCPUs around nodes, map
> the same socket VCPUs to the same NUMA node, which is what
> guest would expect from a sane hardware/BIOS.

"guests"?

> 
> Signed-off-by: Igor Mammedov <address@hidden>

Regards,
Andreas

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