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

[Austin S Hemmelgarn <ahferroin7@xxxxxxxxx>]

On 07/16/2014 01:01 PM, Gordan Bobic wrote:
> On 2014-07-16 16:01, Austin S Hemmelgarn wrote:
>> I hadn't thought about this before now, but part of my results may be
>> because my desktop is running Gentoo with very aggressive optimizations
>> for the specific processor, whereas the Intel server is running Fedora
>> 20, which just uses -O2 -mtune=generic for optimizations.
> 
> Different optimization levels make relatively minor differences. It's
> when you switch to a compiler that does vectorization properly (e.g. ICC)
> that you see significant performance increases.
> 
I would like to point out, ICC used to do some really dirty tricks to
prevent code built with from running at peak efficiency on non-Intel
processors.  Also, the only reason that I still use GCC is because not
everything builds correctly with Clang.
>> Another
>> factor might be that most of my workloads, and therefore most of the
>> benchmarking that I do, are memory-bound, and even though both systems
>> use DDR3-1600 memory, the server is a NUMA system and has the memory
>> split between the two processors.
> 
> That can make a difference, depending on how good the scheduler is
> at migrating process to the memory rather than remote accessing
> the memory.
>
Linux is generally pretty good at this, but doesn't bind
processes/threads to a given core unless the app or the administrator
explicitly tells it to, which means that the memory migration still
hurts latency/throughput.
>> Just comparing processors of similar price from AMD and Intel, you will
>> almost always get a better processor from AMD.  It may not always have
>> the most up-to date set of ISA extensions, but that hardly matters when
>> running Windows because Windows won't try to take advantage of anything
>> that came out after that version of Windows (which is why XP's
>> performance sucks compared to Win7 on newer systems).
> 
> I never noticed this at all. Bloat and feature creep vastly outweighs
> relatively marginal benefits from minor ISA extensions. Consider that
> x86-64 features SSE (there is no x86-64 CPU that doesn't have SSE),
> which makes a big difference _if you use it_ (which most compilers do
> a very poor job of), but jumps to SSE2 and further make relatively
> little difference). So if you are running XP x64 there is going to be
> very little performance from compiler output compared to, say, Windows
> 7 x64.
> 
>
AVX actually does provide a measurable improvement over SSE*, and a lot
of the bit-field manipulation extensions (LZCNT, POPCNT, BMI, TBM, etc)
can provide a very significant boost in performance over processors that
don't have them.
> 
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