Re: [PATCH 3/8] nvptx -muniform-simt

[Alexander Monakov <amonakov at ispras dot ru>]

Ping.

On Mon, 13 Jun 2016, Alexander Monakov wrote:
> On Sun, 12 Jun 2016, Sandra Loosemore wrote:
> > On 06/09/2016 10:53 AM, Alexander Monakov wrote:
> > > +@item -muniform-simt
> > > +@opindex muniform-simt
> > > +Generate code that allows to keep all lanes in each warp active, even when
> > 
> > Allows *what* to keep?  E.g. what is doing the keeping here?  If it is the
> > generated code itself, please rephrase as
> > 
> > Generate code that keeps....
> 
> Let me try to expand and rephrase what I meant:
> 
> Allows the compiler to emit code that, at run time, may have all lanes active,
> particularly in those regions of the program where observable effects from
> execution must happen as if one lane is active (outside of SIMD loops).
> 
> But nevertheless generated code can run just like conventionally generated
> code does: with each lane being active/inactive independently, and side
> effects happening from each active lane (inside of SIMD loops).
> 
> Whether it actually runs in the former (let's call it "uniform") or the latter
> ("conventional") way is switchable at run time. The compiler itself is
> responsible for emitting mode changes at SIMD region boundaries.
> 
> Does this help? Below I went with your suggestion, but changed "keeps" to "may
> keep" because that's generally true only outside of SIMD regions.
> 
> > > +observable effects from execution should appear as if only one lane was
> > 
> > s/was/is/
> > 
> > > +active. This is achieved by instrumenting syscalls and atomic instructions
> > > in
> > > +a lightweight way that allows to switch behavior at runtime. This code
> > 
> > Same issue here....  allows *what* to switch behavior?  (And how would you
> > select which run-time behavior you want?)
> 
> Sorry. This gives compiler itself a way to emit code that will switch behavior
> of the subsequently running code.
> 
> > Also, in the snippet above where it is used as a noun, please
> > s/runtime/run time/
> 
> Thanks. Does the following look better?
> 
> @item -muniform-simt
> @opindex muniform-simt
> Generate code that may keep all lanes in each warp active, even when
> observable effects from execution must appear as if only one lane is active.
> This is achieved by instrumenting syscalls and atomic instructions in a
> lightweight way, allowing the compiler to emit code that can switch at run
> time between this and conventional execution modes. This code generation
> variant is used for OpenMP offloading, but the option is exposed on its own
> for the purpose of testing the compiler; to generate code suitable for linking
> into programs using OpenMP offloading, use option @option{-mgomp}.
> 
> Alexander