Re: [gentoo-dev] New project: LLVM

["C Bergström" <cbergstrom@pathscale.com>]

On Sat, Aug 20, 2016 at 4:52 AM, james <garftd@verizon.net> wrote:

<snip>

>> Back to my own glass house.. It will take a few years, but I am trying
>> to make it easier (internally) to expose in some clear way all the
>> pieces which compose a fine tuning per-processor. If this was "just"
>> scheduling models it would be really easy, but it's not.. Those
>> latencies and other magic bits decide things like.. "should I unroll
>> this loop or do something else" and then you venture into the land of
>> accelerators where a custom regalloc may be what you really need and
>> *nothing* off the shelf fits to meet your goals.. (projects like that
>> can take 9 months and in the end only give a general 1-5% median
>> performance gain..)
>
>
> If this is your mantra, I resend the generous comments. Cray use to work
> that way, milking the Petroleum Industry for tons of money, but, things have
> changed and the change is accelerating, rapidly. Perhaps too much off those
> Cray patents that your company owns are leaking toxins into the brain-trust
> where you park?
>
> Vendor walk-back is sad, imho. ymmv.
>
> Best of luck to your company's  5-year plan....

I have no idea what on earth you were trying to say in most of your
reply. I am speaking only from a compiler perspective. Nothing more
and nothing less.. it may be my difficultly to describe the target
level and processor specific optimization choices a compiler *must*
make.

Beyond not understanding your email, I found it insulting. So please
keep rude comments to yourself.

So again to try to explain the technical side of this - We can't and
have no desire to optimize for every class of processor on the planet.
We have a narrow band of focus on mostly HPC centric code patterns and
processors which are are typically used in HPC workloads. I'd love to
expand past this, but we're a small company and that's our niche.
There's no walking back or trying to claim to be something we're not..
this is pure honest transparency. (imagine it like - do one thing and
do it well)

The only special note I'd add on to this - the CPU isn't where we
spend most of our time tuning, it's by far more on the accelerator
support.