On Wed, Jun 1, 2016 at 4:58 PM, Eero Tamminen <eero.t.tammi...@intel.com> wrote:
> Hi, > > On 01.06.2016 16:53, Marek Olšák wrote: > >> On Wed, Jun 1, 2016 at 3:02 PM, ⚛ <0xe2.0x9a.0...@gmail.com> wrote: >> >>> On Wed, Jun 1, 2016 at 2:19 PM, Marek Olšák <mar...@gmail.com> wrote: >>> >>>> I'll let you figure it out by yourself. >>>> >>> >>> Why would you withhold information if you already have it? Are you a >>> "bad person" or something? >>> >>> As far as my memory goes, I have never posted the sentence "I'll let >>> you figure it out by yourself" to the Internet because I believe it is >>> wrong. >>> >> >> :) >> >> Shader compilation at game loading time is never a problem, so we can >> ignore that. >> > > Startup time may not be a problem for games (some gamers may disagree), > but there are also devices which have legal / certification requirements > for startup times, where shader compilation time could be a problem, > especially as Mesa shader compilation tends to get slower over time (as > compiler does more optimizations). > > Those devices have pretty static content (at least for startup), so their > shaders could be pre-compiled if 3D driver supports that and has offline > compiler. Many proprietary drivers do, Mesa doesn't, at least not yet. > > > Shader compilation right before draw calls is what's unpleasant and >> when people talk about it in the negative sense, they mean this. >> >> Because of external factors you can't predict, your driver suddenly >> receives a bunch of shaders that take 2000 ms to compile right before >> a draw call. Your budget is 16 ms per frame to get 30 fps, but you >> can't render the frame if you don't compile those shaders. The problem >> is how to fit the compilation that takes 2000 ms and is required >> render the frame into 16 ms. Can you see where I'm going? >> > > Besides application itself compiling a shader, some state change done by > application may also trigger shader recompile in Mesa. While for > application requested compilation nothing can be done to squeeze it into > 16ms, there are some chances of reducing need for state-change triggered > recompiles (and these improvements have been done to Mesa during the years). radeonsi doesn't do state-change triggered recompiles since LLVM 3.8. I think nv50/nvc0 doesn't do that either, though I do understand this is a very serious issue with other drivers. The real problem for us (radeonsi specifically) is that some apps really load shaders right before they wanna use them. Marek PS: My mistake, 16 ms is a requirement for 60 fps, not 30.
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