Re: [Xen-users] HTPC + DUAL PC In one

[Austin S Hemmelgarn <ahferroin7@xxxxxxxxx>]

Hyper-Threading shares a lot more than just the FPU between threads,
IIRC the only thing in HT that isn't potentially shared is the
registers, so unless the OS is built to schedule intelligently,
performance on a HT cpu can be really terrible.

Also, just an aside, the FPU on a given module on Bulldozer based CPU's
(like the FX-8350) is only shared for 256-bit vector operations.  If you
are using something like Gentoo, you can build your packages with the
GCC option '-mprefer-avx128' to force the usage of 128-bit vector ops,
and the system will behave like each core has it's own FPU.

Also, as a second aside, Xen makes very little usage of the FPU, and
most non-media non-number-crunching stuff on Linux doesn't use it much
either.
On 07/16/2014 07:51 AM, Mattia Carrara wrote:
> Thanks for the suggestions Gordan!
> 
> So a zfs server properly configured can be an alternative to unRaid?
> 
> This is interesting. So i can partitioning the CPU in multiple virtual
> cores and Xen will manage the schedule?
> I such way i can do something like this: 4 cores for me, 2 cores for my
> family, 1 core for HTPC, 1 core for Dom0; correct? But there's still
> that question, is better an 8core FX-8350 or 4-core i7 4790k? I did some
> research and find that FX-8350 is made of 4 modules with 2 cores each.
> Each module share the same floating point unit and here's the problem: a
> core has to wait for the floating point unit of its module if it is busy
> with the other core. Intel instead uses HyperThreading: the 4790k,
> bacause of this, has 4 cores with 8 threads. I really don't know what to
> do! What do you think?
> 
> 
> 
> 2014-07-16 12:27 GMT+02:00 Gordan Bobic <gordan@xxxxxxxxxx
> <mailto:gordan@xxxxxxxxxx>>:
> 
>     On 2014-07-16 11:12, Mattia Carrara wrote:
> 
>         Hello again Guys. I looked up that HP Microserver, it is pretty cool
>         and cheap. Now I have a limited budged so i will remain on
>         virtualized
>         HTPC. Maybe in the future it will be useful. 
> 
> 
>     It's cheaper than a decent GPU. :)
> 
> 
>         Gordan what is a ZFS reciever?
> 
> 
>     The question was referring to ZFS' send/receive feature. With it
>     you can easily send and receive file system and volume snapshots
>     between different machines.
> 
>         About CPUs, I find on the net some benchmarks:
>         
> http://www.cpubenchmark.net/__compare.php?cmp[]=1780&cmp[]=__1782&cmp[]=2275
>         
> <http://www.cpubenchmark.net/compare.php?cmp[]=1780&cmp[]=1782&cmp[]=2275>
>         [2]
> 
>         It seems that i7 is more performant than AMDs... But the point
>         is that
>         using Xen and multiple virtual machines, i'll need more parallel
>         calculus power, right? So 8 cores would be better? Is it
>         possible that
>         those benchmarks aren't done using all the eight cores of AMDs?
>         Austin
>         said that he can reach the calculus power of a dual processor Xeon
>         E3-1286 v3. That's really a good result. So maybe i should choose
>         AMD...
> 
> 
>     How many cores are you going to give to your VMs? You can overbook
>     CPU cores with Xen, i.e. if you have 8 cores and 3 VMs, you can give
>     each VM 4 cores and Xen will figure out dynamically which core to
>     schedule the load on, even though it only has 8 physical cores to
>     schedule 12 virtual cores plus itself between.
> 
> 
> 
> 
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