Re: [PATCH v9 1/9] xen: vnuma topology and subop hypercalls

From: Elena Ufimtseva <ufimtseva@gmail.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Keir Fraser <keir@xen.org>,
	Ian Campbell <Ian.Campbell@citrix.com>,
	Li Yechen <lccycc123@gmail.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Matt Wilson <msw@linux.com>,
	Dario Faggioli <dario.faggioli@citrix.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [PATCH v9 1/9] xen: vnuma topology and subop hypercalls
Date: Thu, 4 Sep 2014 23:27:13 -0400	[thread overview]
Message-ID: <CAEr7rXj3GCG7AHwjE6txf4o3O1B_-5X1UTTaCjh-Lf5b13GK3w@mail.gmail.com> (raw)
In-Reply-To: <5406ED620200007800030150@mail.emea.novell.com>

On Wed, Sep 3, 2014 at 4:28 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>> On 03.09.14 at 02:46, <ufimtseva@gmail.com> wrote:
>> On Fri, Aug 29, 2014 at 6:37 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>>> On 29.08.14 at 05:04, <ufimtseva@gmail.com> wrote:
>>>> +static struct vnuma_info *vnuma_init(const struct xen_domctl_vnuma *uinfo,
>>>> +                                     const struct domain *d)
>>>> +{
>>>> +    unsigned int nr_vnodes;
>>>> +    int i, ret = -EINVAL;
>>>> +    struct vnuma_info *info;
>>>> +
>>>> +    nr_vnodes = uinfo->nr_vnodes;
>>>> +
>>>> +    if ( nr_vnodes == 0 || nr_vnodes > uinfo->nr_vmemranges ||
>>>
>>> Is that really a necessary check? I.e. does code elsewhere rely on
>>> that? I ask because memory-less nodes are possible on real
>>> hardware.
>>
>> That is true. But taking into account that there are no buses support
>> yet added, absence of memory and buses for a vNUMA node
>> seem to be useless. And vNUMA can mimic hardware NUMA as close as
>> possible, but I think the degree of this is pretty much our choice.
>> With further extension of vNUMA to include buses I think this check
>> will naturally disappear.
>
> I have to admit that I struggle with the references to "buses" in your
> reply. Could you perhaps give some context (not the least because
> already known future extensions may call for making provisions for
> them in the public interface)?
>
> Jan
>

Sorry Jan, looks like I have missed that one.

I meant NUMA I/O when was referring to buses.
For example from here/
http://en.community.dell.com/cfs-file.ashx/__key/telligent-evolution-components-attachments/13-4491-00-00-20-26-69-46/NUMA-for-Dell-PowerEdge-12G-Servers.pdf

Or here NUMA I/O = PCIe :
http://events.linuxfoundation.org/sites/events/files/eeus13_shelton.pdf

In earlier discussions of vNUMA, numa I/O was mentioned but never
really looked at yet from implementation point of view.

-- 
Elena