Re: NUMA TODO-list for xen-devel

[Dario Faggioli <raistlin@linux.it>]

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On Fri, 2012-08-03 at 15:22 -0700, Dan Magenheimer wrote:
> Hi Dario --
> 
Hello Dan,

> Thanks for your great work on NUMA... an interest area of
> mine but one, sadly, I haven't been able to give much time to,
> so I'm glad you've taken this bull by the horns.
> 
Trying to... Let's see! :-P

> I've been sitting on an idea for some time that probably
> deserves some exposure on your list.  Naturally, it involves
> my favorite topic tmem (readers, please don't tune out yet :-).
> 
It sure does! I've already put something quite generic about "memory
sharing" there, because I know that it has all but trivial interactions
with the improved NUMA support I am/we are trying to envision.

The fact that it is, as I said, generic, is due to my ignorance (let's
say for now) of the whole tmem thing, so thanks for the contribution,
it's very useful to hear your point of view on this!

> It has occurred to me that a fundamental tenet of NUMA
> is to put infrequently used data on "other" nodes, while
> pulling frequently used data onto a "local" node.
> 
> Tmem very nicely separates infrequently-used data from
> frequently-used data with an API/ABI that is now fully
> implemented in upstream Linux.
> 
I see, and it seems nice.

> [..]
>
> Naturally, this doesn't solve any NUMA problems at all for
> tmem-ignorant or tmem-disabled guests, but if it works
> sufficiently well for tmem-enabled guests, that might
> encourage other OS's to do a simple implementation of tmem.
> 
Sure. In my opinion, this is not an area where we could aim at "solving
every problem for everyone". However, we should definitely target having
a sensible solution for default and/or most common use cases and
scenarios.

> Sadly, I'm not able to invest much time in this idea,
> but the combination of tmem and NUMA might interest some
> developers and/or grad students, in which case I'd be happy
> to spend a little time assisting.
> 
That's definitely the case. I've tried to put a summary of what you said
in this mail to the Wiki (http://wiki.xen.org/wiki/Xen_NUMA_Roadmap) and
also put your contact next to it. Feel free to update/correct if you fin
something wrong. :-P

> I'll be at Xen Summit for at least the first day, so we
> can chat more if you are interested.
>
I indeed am interested, so let's make that happen! :-)

Thanks and Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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