consistency, please

By: Michael S (already5chosen.delete@this.yahoo.com), July 11, 2013 2:43 pm
Room: Moderated Discussions
Linus Torvalds (torvalds.delete@this.linux-foundation.org) on July 11, 2013 11:52 am wrote:
>
>
> There's a big difference between SSE and AVX. One is some rather basic vector
> and FP stuff, the other is pretty esoteric and has much less use.
>

Technically, there is nothing esoteric about AVX. It serves exactly the same purpose as SSE, but serves it better. Arguably, AVX, with possible exception of 256-bitness, is what SSE should have been from the day one, if back then Intel architects were smarter.
Scalar/128b AVX enhancements over SSE (more compact and regular encoding and non-destructive operations) even more advantageous for narrow mostly-in-order core like Silvermont than they are for fatter cores, because on such core both # of instructions per task and # of code bytes per task are scarcer.

Now, what is "esoteric" about AVX is ubiquity. Strangely, despite AVX being Intel's baby, Intel is also a main offender here.

> And yes, I'd also claim that any cellphone benchmark that uses
> AVX would be just crazy. Even crazier than using NEON.
>

That's a typical self-fulfilling prophecy. Of course, cellphone benchmark that uses
AVX would remain crazy as long as the only x86 manufacturer capable of making phone-class application processors does not implement AVX in its processors.

> So I absolutely stand by my point: I think it's absolutely insane to expect/want Atom
> to have AVX, when it's not even clear that all new Atoms will be 64-bit enabled. AVX is
> a niche thing that doesn't even make sense in a mobile or microserver environment.
>

So, ours ways of reasoning and our ideas of consistency just differ too much.

> And that is NOT AT ALL inconsistent with me then complaining that ARM doesn't make even
> basic floating point or the most basic vector support something you can really rely on.
>
> Happily, for the kernel, I don't need to care all that deeply. We avoid the use of FP for
> other general reasons, and so we don't see that. But the ARM situation annoys me because this
> whole "incompatible microarchitectures" goes so much deeper than just FP/vector: it's all
> over (Thumb2 or not? yadda yadda), and the whole architecture specification is a mess.
>

If I was you, I'd simply refuse to support new version of full-blown Linux on anything less than v7-A. Those who want to run on older or lesser variants would have to maintain their own forks or to use older versions of the kernel.

But, then again, if I was you, I'd likely have different considerations. As chess commentators used to say, it's easy to sacrifice other player's pieces.
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ARM at Computexanon2013/06/03 08:54 AM
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                                      Saltwell Outperforming A15...With Less Power!!!bakaneko2013/07/12 03:28 AM
                                        Saltwell Outperforming A15...With Less Power!!!Linus Torvalds2013/07/12 09:11 AM
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                                                How'd you get this flower symbol as your user name ?anon2013/07/13 09:20 AM
                                                  How'd you get this flower symbol as your user name ?Doug S Ꭳ❂〄☢⚓♜☎♬⚄☠2013/07/13 10:12 AM
                                                JITx2013/07/15 06:43 AM
                                    Not reallyAnon2013/07/11 11:21 AM
                                    consistency, pleaseMichael S2013/07/11 11:22 AM
                                      consistency, pleaseLinus Torvalds2013/07/11 11:52 AM
                                        consistency, pleaseMichael S2013/07/11 02:43 PM
                                          consistency, pleaseLinus Torvalds2013/07/11 03:12 PM
                                            consistency, pleaseMark Roulo2013/07/11 03:54 PM
                                              the discussion was about absence of AVX in Silvermont (NT)Michael S2013/07/11 03:59 PM
                                                the discussion was about absence of AVX in SilvermontMark Roulo2013/07/11 04:19 PM
                                                  the discussion was about absence of AVX in SilvermontLinus Torvalds2013/07/12 09:16 AM
                                                    Thank youMark Roulo2013/07/12 09:58 AM
                                                    the discussion was about absence of AVX in Silvermontanon2013/07/12 10:10 AM
                                                      Not really (again)Anon2013/07/12 10:26 AM
                                                        Not really (again)anon2013/07/12 05:40 PM
                                                    the discussion was about absence of AVX in SilvermontLinus Torvalds2013/07/12 10:31 AM
                                                      you are wrong at about 100% of you saidMichael S2013/07/13 11:22 AM
                                                        you are wrong at about 100% of you saidLinus Torvalds2013/07/13 12:08 PM
                                                          you are wrong at about 100% of you saidMichael S2013/07/13 01:13 PM
                                                            you are wrong at about 100% of you saidLinus Torvalds2013/07/13 02:11 PM
                                                            you are wrong at about 100% of you saidvvid2013/07/13 03:20 PM
                                                              you are wrong at about 100% of you saidMichael S2013/07/14 01:38 AM
                                    Saltwell Outperforming A15...With Less Power!!!anon2013/07/11 06:41 PM
                                    Saltwell Outperforming A15...With Less Power!!!bakaneko2013/07/12 03:22 AM
                  Round 2: Baytrail benchmark (yes Antutu!) crushes Snapdragon 800.sammy2013/07/12 11:28 AM
                    Round 2: AnTuTu scores drop dramatically for AtomWilco2013/07/12 11:59 AM
                      Round 2: AnTuTu scores drop dramatically for AtomSteve2013/07/14 08:16 PM
                        Round 2: AnTuTu scores drop dramatically for AtomKlimax2013/07/14 10:59 PM
                        Round 2: AnTuTu scores drop dramatically for AtomDavid Kanter2013/07/15 01:57 PM
                          Intel is cheating AnTuTuWilco2013/07/15 03:43 PM
                            Intel is cheating AnTuTubakaneko2013/07/15 07:47 PM
                              Intel is cheating AnTuTuLinus Torvalds2013/07/15 08:45 PM
                                Intel is cheating AnTuTubakaneko2013/07/16 02:42 AM
                                  Intel is cheating AnTuTuWilco2013/07/16 03:47 AM
                                    Intel is cheating AnTuTubakaneko2013/07/16 05:50 AM
                                      Intel is cheating AnTuTuWilco2013/07/17 03:33 PM
                                        Intel is cheating AnTuTuKlimax2013/07/17 11:29 PM
                                          Intel is cheating AnTuTunone2013/07/17 11:35 PM
                                            Intel is cheating AnTuTuKlimax2013/07/18 01:41 AM
                                              Intel is cheating AnTuTuanon2013/07/18 02:10 AM
                                                Intel is cheating AnTuTuMichael S2013/07/18 03:39 AM
                                                Intel is cheating AnTuTuWilco2013/07/18 04:07 AM
                                                  Intel is cheating AnTuTunone2013/07/18 04:15 AM
                                                    Intel is cheating AnTuTuWilco2013/07/18 05:18 AM
                                                    Intel is cheating AnTuTuMichael S2013/07/18 06:44 AM
                                                      Intel is cheating AnTuTunone2013/07/18 07:47 AM
                                                        strict aliasingMichael S2013/07/18 08:10 AM
                                                          strict aliasing rules have existed since C89 (NT)Ricardo B2013/07/18 05:28 PM
                                                  Intel is cheating AnTuTuKlimax2013/07/18 11:30 AM
                                                Intel is cheating AnTuTuKlimax2013/07/18 11:39 AM
                                                  Intel is cheating AnTuTuanon2013/07/18 12:05 PM
                                                    Intel is cheating AnTuTuKlimax2013/07/20 12:05 AM
                                                      Intel is cheating AnTuTunone2013/07/20 02:50 AM
                                                  Intel is cheating AnTuTunone2013/07/18 12:38 PM
                                                    Intel is cheating AnTuTuKlimax2013/07/19 11:57 PM
                                  Intel is cheating AnTuTuLinus Torvalds2013/07/16 12:32 PM
                                Intel is cheating AnTuTu2013/07/16 03:16 AM
                                  Intel is cheating AnTuTubakaneko2013/07/16 04:55 AM
                                    Intel is cheating AnTuTuWilco2013/07/17 03:46 PM
                                      Intel is cheating AnTuTubakaneko2013/07/18 02:05 PM
                                      Intel is cheating AnTuTuDavid Kanter2013/07/19 02:31 AM
                          Round 2: AnTuTu scores drop dramatically for Atomanon2013/07/15 04:43 PM
                            Round 2: AnTuTu scores drop dramatically for Atomnone2013/07/16 12:15 AM
                          Round 2: AnTuTu scores drop dramatically for AtomGroo2013/07/16 07:35 AM
        ARM at Computexanon2013/06/04 10:43 PM
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