By: Doug S (foo.delete@this.bar.bar), October 30, 2016 12:20 pm
Room: Moderated Discussions
Wilco (Wilco.Dijkstra.delete@this.ntlworld.com) on October 30, 2016 5:00 am wrote:
> There is nothing 8 wide in x86 cores - you can't count micro-op or macro-op
> fusion as making a CPU wider. In fact Apple's cores are significantly wider
> than Intel's both in the front-end and back-end. It's 4 vs 6 and 7 vs ~10.
Why not? The fact that Intel's instruction set is CISC means that some instructions encode more than one RISC instruction. So if 4 x86 instructions can decode to 8 RISC instructions, and can be executed them all at once, I'd argue that it is technically an 8 wide front end - just one with a lot of issue restrictions because you have to have the 'right' 8 instructions for it to work. No different than the fact that Apple's front end can't handle every possible combination of 6 instructions, but are limited in some ways.
If you had a CPU that could execute 11 instructions at once, so long as they were register moves, but a maximum of 3 if anything other than a register move was included, would you consider it 3 wide or 11 wide? Every wide modern core has various restrictions in place, so every number for front/back end width has to come with an asterisk.
> There is nothing 8 wide in x86 cores - you can't count micro-op or macro-op
> fusion as making a CPU wider. In fact Apple's cores are significantly wider
> than Intel's both in the front-end and back-end. It's 4 vs 6 and 7 vs ~10.
Why not? The fact that Intel's instruction set is CISC means that some instructions encode more than one RISC instruction. So if 4 x86 instructions can decode to 8 RISC instructions, and can be executed them all at once, I'd argue that it is technically an 8 wide front end - just one with a lot of issue restrictions because you have to have the 'right' 8 instructions for it to work. No different than the fact that Apple's front end can't handle every possible combination of 6 instructions, but are limited in some ways.
If you had a CPU that could execute 11 instructions at once, so long as they were register moves, but a maximum of 3 if anything other than a register move was included, would you consider it 3 wide or 11 wide? Every wide modern core has various restrictions in place, so every number for front/back end width has to come with an asterisk.
Topic | Posted By | Date |
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Neat die area comparison image | anonymou5 | 2016/10/21 06:44 PM |
Neat die area comparison image | Mr. Camel | 2016/10/22 04:58 AM |
Neat die area comparison image | Heikki Kultala | 2016/10/22 05:19 AM |
Neat die area comparison image | Mr. Camel | 2016/10/22 07:10 AM |
Neat die area comparison image | Mr. Camel | 2016/10/22 07:15 AM |
different caches... | Heikki Kultala | 2016/10/22 08:29 AM |
Broadwell includes LLC, just for comparision | anon | 2016/10/22 08:52 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/23 06:09 AM |
Broadwell includes LLC, just for comparision | anon | 2016/10/23 07:25 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/25 09:57 AM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/10/25 11:03 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/28 02:02 AM |
Broadwell includes LLC, just for comparision | anon | 2016/10/28 04:13 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/29 09:47 PM |
Broadwell includes LLC, just for comparision | Travis | 2016/10/30 06:34 PM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/31 04:35 AM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/10/31 04:42 AM |
Broadwell includes LLC, just for comparision | anon | 2016/11/01 12:56 PM |
Broadwell includes LLC, just for comparision | Maynard Handley | 2016/11/01 01:37 PM |
Broadwell includes LLC, just for comparision | anon | 2016/11/01 04:22 PM |
Broadwell includes LLC, just for comparision | Maynard Handley | 2016/11/01 07:30 PM |
Broadwell includes LLC, just for comparision | anon | 2016/11/02 06:15 AM |
Broadwell includes LLC, just for comparision | Maynard Handley | 2016/11/02 09:23 AM |
Broadwell includes LLC, just for comparision | anon | 2016/11/02 11:50 AM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/11/02 02:48 AM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/10/28 06:19 AM |
Broadwell includes LLC, just for comparision | juanrga | 2016/10/29 10:15 PM |
Broadwell includes LLC, just for comparision | Simon Farnsworth | 2016/10/30 12:31 PM |
Broadwell includes LLC, just for comparision | Ricardo B | 2016/10/29 05:30 PM |
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That wasn't the point | juanrga | 2016/10/28 02:15 AM |
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8 wide vs 6 wide | Wilco | 2016/10/30 05:00 AM |
8 wide vs 6 wide | Doug S | 2016/10/30 12:20 PM |
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