On Mon, Sep 19, 2011 at 10:29:15PM -0700, Keith Packard wrote: > On Mon, 19 Sep 2011 21:25:03 -0700, Ben Widawsky <b...@bwidawsk.net> wrote: > > When doing a GTT mapping, the pages are not backed until taking a fault. > > If we know that the object is write only, when the fault happens we do not > > need > > to make the pages coherent with the CPU. This allows for semi fast > > prefaults > > to occur in libdrm at map time. > > Every time I see this stuff, I get confused by the term > 'write-only'. Reading through the code, I remind myself that what you're > actually promising is that any CPU accesses to the object will not > overlap any potential writes by the GPU. The CPU could be reading or > writing, it really doesn't matter.
I think of it as, we (libdrm + kernel) promise that the buffer is not guaranteed to be coherent with the GPU. Mesa/client is who should be making the promise to not write to a part of the buffer that the GPU may be accessing. > > Really what you want is a kernel call that does everything except block > on the GPU, right? Yes, exactly. Ben
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