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Re: [Qemu-devel] [PATCH V17 00/11] Add support for binding guest numa no
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH V17 00/11] Add support for binding guest numa nodes to host numa nodes |
Date: |
Mon, 09 Dec 2013 18:33:41 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9 |
Il 06/12/2013 19:49, Marcelo Tosatti ha scritto:
>> > You'll have with your patches (without them it's worse of course):
>> >
>> > RAM offset physical address node 0
>> > 0-3840M 0-3840M host node 0
>> > 4096M-4352M 4096M-4352M host node 0
>> > 4352M-8192M 4352M-8192M host node 1
>> > 3840M-4096M 8192M-8448M host node 1
>> >
>> > So only 0-3G and 5-8G are aligned, 3G-5G and 8G-8.25G cannot use
>> > gigabyte pages because they are split across host nodes.
> AFAIK the TLB caches virt->phys translations, why specifics of
> a given phys address is a factor into TLB caching?
The problem is that "-numa mem" receives memory sizes and these do not
take into account the hole below 4G.
Thus, two adjacent host-physical addresses (two adjacent ram_addr_t-s)
map to very far guest-physical addresses, are assigned to different
guest nodes, and from there to different host nodes. In the above
example this happens for 3G-5G.
On second thought, this is not particularly important, or at least not
yet. It's not really possible to control the NUMA policy for
hugetlbfs-allocated memory, right?
>> > So rather than your patches, it seems simpler to just widen the PCI hole
>> > to 1G for i440FX and 2G for q35.
>> >
>> > What do you think?
>
> Problem is its a guest visible change. To get 1GB TLB entries with
> "legacy guest visible machine types" (which require new machine types
> at the host side, but invisible to guest), that won't work.
> Windows registration invalidation etc.
Yeah, that's a tradeoff to make.
Paolo
> But for q35, sure.
>
- [Qemu-devel] [PATCH V17 10/11] NUMA: add qmp command query-numa, (continued)
Re: [Qemu-devel] [PATCH V17 00/11] Add support for binding guest numa nodes to host numa nodes, Paolo Bonzini, 2013/12/06