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Re: [Qemu-devel] [PATCH v2 for-2.3] numa: pc: fix default VCPU to node m
From: |
Andreas Färber |
Subject: |
Re: [Qemu-devel] [PATCH v2 for-2.3] numa: pc: fix default VCPU to node mapping |
Date: |
Thu, 19 Mar 2015 17:05:13 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
Am 18.03.2015 um 17:38 schrieb Igor Mammedov:
> since commit
> 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
> 2.6.32 based kernels will hang on boot due to incorrectly build
> 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
> 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.
>
> Signed-off-by: Igor Mammedov <address@hidden>
> ---
> v2:
> - add machine callback cpu_index_to_socket_id() and use it
> instead of stub approach
> ---
> hw/i386/pc.c | 9 +++++++++
> include/hw/boards.h | 5 +++++
> include/sysemu/numa.h | 3 ++-
> numa.c | 18 +++++++++++++-----
> vl.c | 2 +-
> 5 files changed, 30 insertions(+), 7 deletions(-)
Looks great to me now, the hook name with _socket_id is perfect,
Reviewed-by: Andreas Färber <address@hidden>
but can we do that in three steps please? "machine:" adding callback and
default implementation, "numa:" switching to use it and "pc:" overriding
the new callback - not only nicer subjects but easier to cherry-pick and
bisect then.
Regards,
Andreas
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