2009/9/23 Kenneth Ostby <[email protected]>: > Hi, > > Nicolas Boulay: >>2009/9/23 Hugh Fisher <[email protected]>: >>> Andre Pouliot wrote: <...> >> >>Personnaly LIW is what i prefer : exposed every unit of the shader in >>the instruction word. Then it became a software challenge to optimise >>them. > > I'm unsure if LIW is the good option for this architecture. This due to > the fact that Andre mentioned earlier, we have a lot of threads that > needs to to execute the same instruction over data in close spatial > locality. Hence, there is really no use in having fine grained control > over the different units in a single shader, since in most cases they > are going to execute the same instruction anyways. Thus, including LIW > will only increase the complexity of the hardware, without providing any > substantial gains. >
I doesn't understand your point. That means that the ALU will be full but the other unit will be unused ? for example adder and multiplication could be a separat unit, both could be filled in the same time (MAC instead of MUL + an adder should be better). >> >>One other solution is having word aligned instructions. So you could >>have 32, 64, 128 bits instructions size. > > Before we decide on the length of the instruction, it would be fun to > further investigate some stuff from real life. And this is where we can > benefit from some of the software dudes out there. I would like to see > how big the average shader code is, compared to the available memory we > have on the underlying technology. Cause due to my initial calculations > here, if we assume 32'000 instructions in a kernel( Which from what I > have seen is a lot ), we use about 250KB [1] to store it using 64 bit > instruction words. That also leaves us with a lot of flexibility in the > instruction word, and the decoding should really not be that hard > either. However, depending on the underlying technology, 250KB might be > a lot of RAM. > > [1] ( 32000 * 8 ) / 1024 > I hope you could put more than a single RISC instruction on 64 bits ! If you take 3 "basic" instructions in 64 bits. You should divide your result by 3. > -- > Life on the earth might be expensive, but it > includes an annual free trip around the sun. > > Kenneth Østby > http://langly.org > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.9 (GNU/Linux) > > iEYEARECAAYFAkq54p4ACgkQpcFZhY+VljxDYgCgi9tmcoku1boYNMFw3gJ93nZk > N/UAnReixt2zNaaOf82pZyWtXQ5H+Nz1 > =gJvw > -----END PGP SIGNATURE----- > > _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
