Matt Turner <matts...@gmail.com> writes: > On Wed, Mar 11, 2015 at 2:29 PM, Francisco Jerez <curroje...@riseup.net> > wrote: >> Matt Turner <matts...@gmail.com> writes: >>> commit 4c4934636cb286e7d7836afc26e9d392e2f0f155 >>> Author: Paul Berry <stereotype...@gmail.com> >>> Date: Tue Sep 24 15:18:52 2013 -0700 >>> >>> i965/blorp: retype destination register for texture SEND instruction to >>> UW. >>> >>> The resource streamer only exists on HSW+, so the UW dest is certainly >>> needed for things after Gen5. >> >> Odd, I haven't seen a mention of that restriction in the hardware specs >> (at least not on reasonably recent ones -- the Gen4 and 5 specs do >> mention it and they actually hang if you send a message with compression >> enabled and anything bigger than a W as destination type). Is this a >> purely empirical finding? If so, doesn't it deserve a big fat warning >> comment? Is this only a problem for some interaction with the resource >> streamer or has it ever been observed to fix something else? > > This page [0] says: > > """ > The subregister number, horizontal stride, destination mask and type > fields of <dest> are always valid and are used in part to generate the > WrEn. This is true even if <dest> is a null register (this is an > exception for null as for most cases these fields are ignored by > hardware). These parameters of <dest> follow the same restriction as > that of normal destination operand – destination region cannot cross > the 256-bit register boundary. > """ > > Searching for the exact phrase quoted in Paul's commit finds another > page that says it applies to "DevSNB+,Pre-DevBDW". >
Hm, searching for the same phrase ("destination region cannot cross the 256-bit register boundary.") gives several matches, some of the pages are indeed tagged "DevSNB+,Pre-DevBDW", but in all of them that phrase appears inside a SNB-only block, I don't see any indication of that restriction applying to Gen7 and up. > I think this is one of those cases where they technically give you all > the information, they just don't tell you anything about what you're > supposed to do with it. Totally bullshit, but par for the course. > > I guess the good news in all of this is that we now know we don't need > to bother with this for BDW+. > > [0] 3D-Media-GPGPU Engine > EU Overview > ISA Introduction > > Instruction Set Reference > EUISA Instructions > Send Message [SNB+]
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