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

[Paolo Bonzini <pbonzini@redhat.com>]

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?

Paolo