Messages in this thread |  | | From | Jesse Barnes <> | Subject | Re: [PATCH] x86: create array based interface to change page attribute | Date | Tue, 8 Apr 2008 07:27:27 -0700 |
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On Monday, April 07, 2008 11:21 pm Thomas Hellström wrote: > 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.
Hm, yeah, anholt was telling me about some of these cases offline too. This is what makes things really difficult...
Jesse -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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