Messages in this thread |  | | Date | Tue, 08 Apr 2008 08:21:28 +0200 | From | Thomas Hellström <> | Subject | Re: [PATCH] x86: create array based interface to change page attribute |
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Jesse Barnes wrote: > On Monday, April 07, 2008 1:46 pm Thomas Hellström wrote: > >>> Why would we need to flush at all at unbind-read-bind time? We should be >>> able to leave pages in the WC state even when we unbind them, then when >>> we need to bind them back into the GTT they'll be ready, but maybe I'm >>> misunderstanding you here... >>> >> We want to make the user-space mapping cache-coherent after unbind >> during read, to have any serious read-speed, and the linear kernel map >> has to follow, unless it's non-present. Even if it's non present, we >> need to flush whatever was written through the user-space mapping from >> the cache when rebinding. Having the user-space mapping read-only when >> possible will help avoid this. >> > > Ah, you actually want to *read* from memory? Yeah that would be really slow > if we left it UC or WC. But I thought that was really only necessary for > relocation, and keithp dealt with that with the "presumed offset" stuff? Are > you seeing other cases where we need to read back frequently? > While keithp's "presumed offset" is really good stuff, we should never need to read from device memory during relocations, I think. I was thinking of EXA and OpenGL software fallback cases, "download from screen" and "readpixels" types of operation, as well as pixel-buffer-object map in read mode.
/Thomas
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