consistency, please

By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), July 11, 2013 3:12 pm
Room: Moderated Discussions
Michael S (already5chosen.delete@this.yahoo.com) on July 11, 2013 2:43 pm wrote:
>
> Technically, there is nothing esoteric about AVX

I'd argue that AVX is esoteric for one simple reason: it assumes that vectors are so important that you want to waste tons of resources on them.

And don't try to make out like it's not tons of resources. Yes, you can make a fairly bad implementation of AVX (ie not true 256-wide units), but even that is nasty for resource tracking and the pipeline, and it wouldn't actually generally be any faster than XMM, and so the people who want AVX would complain anyway.

So it's almost certainly better to just not fake it, since there isn't all that big an installed base for it anyway.

Yes, yes, I'm a single-thread and scalar bigot. I'll happily admit to that. I think vectorization has an upside, but I don't happen to think that it is all that big, and I think there are quickly diminishing returns. I just happen to think that AVX crossed the line on that "effort vs returns" scale, which is why I think the lack of AVX support in Atom is quite reasonable.

But yes, since AVX thus isn't something you can rely on in new cpus, that makes it potentially much less interesting to support for many software cases too. And I just don't think it's important enough to matter.

Engineering is about tradeoffs.

Linus
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                                      Saltwell Outperforming A15...With Less Power!!!Sylvain Collange2013/07/12 02:29 AM
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                                          Saltwell Outperforming A15...With Less Power!!!Sylvain Collange2013/07/12 06:00 AM
                                      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
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                                                    Intel is cheating AnTuTuMichael S2013/07/18 06:44 AM
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                                                  Intel is cheating AnTuTuanon2013/07/18 12:05 PM
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                                                  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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