Re: [Qemu-devel] [PATCH V9 06/12] NUMA: Add Linux libnuma detection

[Wanlong Gao <gaowanlong@cn.fujitsu.com>]

On 08/28/2013 09:44 PM, Paolo Bonzini wrote:
> Il 26/08/2013 10:43, Andrew Jones ha scritto:
>>
>> ----- Original Message -----
>>>> On 08/26/2013 03:46 PM, Andrew Jones wrote:
>>>>>>>>>> Is this patch still necessary? I thought that dropping the
>>>>>>>>>>>>>> numa_num_configured_nodes() calls from patch 8/12 got rid
>>>>>>>>>>>>>> of the need for this library. Maybe I missed other uses?
>>>>>>>>>>
>>>>>>>>>> Yes, in 08/12 we also use mbind(),
>>>>>> You don't need a whole library for mbind(), it's a syscall. See syscall(2).
>>>>>>
>>>>>>>>>> and in 09/12 we use max_numa_node().
>>>>>> Really? I didn't see it there. And anyway, that goes back to our discussion
>>>>>> about setting qemu's MAX_NODES to whatever we think qemu should support,
>>>>>> and then just checking that we don't blow that limit whenever reading
>>>>>> host node info, i.e.
>>>>>>
>>>>>> maxnode = 0;
>>>>>> while (host_nodes[maxnode] && maxnode < MAX_NODES)
>>>>>>   node_read(&info[maxnode++]);
>>>>>>
>>>>>> type of a thing.
>>>>>>
>>>>>> And, if there's a place you really need to know the current online number
>>>>>> of host nodes, then, like I said earlier, you should just go to sysfs
>>>>>> yourself. libnuma:numa_max_node() returns an int that it only initializes
>>>>>> at library load time, so it's not going to adapt to onlining/offlining.
>>>>
>>>> OK, thank you.
>>>> Then I should define MPOL_* macros in QEMU and use mbind(2) syscall directly,
>>>> right?
>> Hmm, yeah, that's too bad that numaif.h is part of libnuma, and not a more
>> general lib. Whether or not we want to redefine those symbols within
>> qemu, in order to avoid the dependency on installing numactl-devel, isn't
>> something I can answer. That's a better question for Anthony. Anthony? Paolo,
>> any opinions? Maybe we should pick up uapi/linux/mempolicy.h with the
>> linux-header synch script?
>>
> 
> I think using libnuma is fine.  In principle this could be used on other
> OSes than Linux, I think?

But seems that mbind(2) is Linux-specific syscall, right?

Thanks,
Wanlong Gao

> 
> Paolo
>