Sharing between servers and phones

By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), January 30, 2017 11:01 am
Room: Moderated Discussions
rwessel (robertwessel.delete@this.yahoo.com) on January 29, 2017 8:56 pm wrote:
>
> That's at least partially untrue for zArch. Context switches are very common in MVS*, as many things happen
> via calls to other address spaces (most often mediated by the zArch equivalent of a call gate**). zArch's
> TLBs (and specifically the two level TLBs) are there to avoid needing TLB reloads precisely because address
> space context switches have been increasing significantly in frequency for the last three decades.

Ahh. But afaik s390 at least has address space identifiers, so it's not as deadly for the TLB contents as the old win32 gdi behavior was.

> Much of GDI in Widnows was moved back into the kernel, back in the NT4 days

Oh yes, the insane "TLB switches _all_ the time" behavior was purely a win32 issue, I don't think NT ever had it at least under normal load.

So it's long gone, but the legacy lives on in microarchitectural details.

Also, x86 these days actually has ASIDs (although they are called PCID, which I personally find a particularly annoying NIH acronym, but every single time I read it as "PCI" something). I think they ended up evolving out of having the virtualization support (single-bit tag in the TLB to avoid TLB misses on each VM exit/entry).

We don't actually use it in Linux because it wasn't a noticeable win, probably exactly because the TLB is aggressively prefetched, and outside of virtualization there is very seldom very frequent TLB switches.

(Even the classic "ping pong scheduling benchmark" still runs a lot of code in between TLB flushes, and is not very common behavior anyway. It really takes crazy "function calls between address spaces" to get very high TLB switch behavior).


> As to how the page tables are organized, it's very little like POWER, and quite similar to x86 in gross
> terms (every detail is different, of course).

Yeah, I'm, aware of the high-level details, the oddities are in the low-level issues (very strange TLB flushing, iirc, due to some odd dirty bit handling and other rules, I only see the patches flow by, I've never used it or looked all that closely).

> While fast TLB reloads are certainly a good thing, they are still an expense, avoiding unnecessary discards
> of TLB entries, especially on short switches to different address spaces, compliments that.

No disagreement. Although I personally find that to be more of a SW design issue: people who design their calling conventions to be about cross-process boundaries are crazy.

Linus
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Cray to Develop ARM-based Isambard Supercomputer for UK Met Officegallier201/20/17 08:48 AM
  Cray to Develop ARM-based Isambard Supercomputer for UK Met Officegallier201/20/17 08:48 AM
    Ignore second post (NT)gallier201/20/17 08:49 AM
  ARM-based supercomputersDavid Kanter01/20/17 03:55 PM
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      ARM-based supercomputers lolRobert David Graham01/21/17 06:34 PM
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            ARM-based supercomputers lolMichael S01/22/17 03:07 AM
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          ARM-based supercomputers lolanon01/22/17 03:24 AM
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              ARM-based supercomputers lolanon01/23/17 07:40 AM
            ARM-based supercomputers loljuanrga01/29/17 06:01 AM
              ARM-based supercomputers lolanon01/29/17 10:35 AM
        ARM-based supercomputers lolBrendan01/21/17 08:36 PM
         Dumb belief? ROFL (NT)juanrga01/22/17 03:59 AM
          Dumb belief? ROFLwumpus01/22/17 12:31 PM
            Dumb belief? ROFLjuanrga01/29/17 06:13 AM
        ARM-based supercomputers lolDavid Kanter01/22/17 09:20 AM
    ARM-based supercomputersRichardC01/22/17 08:54 AM
      ARM-based supercomputersAaron Spink01/22/17 01:03 PM
        ARM-based supercomputersNiels Jørgen Kruse01/22/17 01:16 PM
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            ARM-based supercomputersNiels Jørgen Kruse01/23/17 11:41 PM
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              A73 does not have L1 ECCdmcq01/24/17 09:15 AM
                A73 does not have L1 ECCMichael S01/24/17 09:47 AM
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          ARM-based supercomputersAaron Spink01/23/17 08:02 PM
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              X-Gene 3 supports 1TB of memoryWilco01/24/17 03:13 AM
                You seem to be confusing "SoC" with "CPU core" (NT)Anon01/24/17 04:12 AM
                X-Gene 3 supports 1TB of memoryMichael S01/24/17 06:26 AM
                  X-Gene 3 supports 1TB of memorydmcq01/24/17 09:28 AM
                X-Gene 3 supports 1TB of memoryAaron Spink01/24/17 07:46 AM
                  X-Gene 3 supports 1TB of memoryWilco01/24/17 04:10 PM
                    X-Gene 3 supports 1TB of memoryDavid Kanter01/24/17 08:31 PM
                X-Gene 3 supports 1TB of memorySimon Farnsworth01/26/17 03:23 AM
              X-Gene 3 supports 1TB of memoryAaron Spink01/24/17 07:44 AM
                X-Gene 3 supports 1TB of memoryAnon01/24/17 02:54 PM
                  X-Gene 3 supports 1TB of memoryWilco01/24/17 04:07 PM
                    X-Gene 3 supports 1TB of memoryDavid Kanter01/24/17 08:34 PM
                      X-Gene 3 supports 1TB of memorynone01/24/17 11:48 PM
                        X-Gene 3 supports 1TB of memoryMichael S01/25/17 02:32 AM
                        X-Gene 3 supports 1TB of memoryDavid Hess01/25/17 10:47 PM
                          X-Gene 3 supports 1TB of memoryMichael S01/26/17 01:55 AM
                            Really that different?Daniel B01/26/17 04:37 AM
                              Really that different?none01/26/17 06:39 AM
                                Really that different?itsmydamnation01/26/17 04:55 PM
                                  Really that different?none01/27/17 12:14 AM
                      X-Gene 3 supports 1TB of memoryWilco01/25/17 04:22 AM
                        Sharing between servers and phonesDavid Kanter01/25/17 08:15 AM
                          Sharing between servers and phonesWilco01/25/17 05:41 PM
                            Sharing between servers and phonesDavid Kanter01/25/17 07:10 PM
                              Sharing between servers and phonesGabriele Svelto01/26/17 04:15 AM
                                Sharing between servers and phonesDavid Kanter01/26/17 08:33 AM
                                  Sharing between servers and phoneswumpus01/26/17 04:25 PM
                                    Sharing between servers and phonesDavid Kanter01/27/17 07:46 AM
                                      Any idea why Intel doesn't ship server chips with eDRAM?Mark Roulo01/27/17 10:02 AM
                                        Any idea why Intel doesn't ship server chips with eDRAM?Per Hesselgren01/28/17 07:49 AM
                                          Any idea why Intel doesn't ship server chips with eDRAM?Simon Farnsworth01/28/17 08:06 AM
                                          Any idea why Intel doesn't ship server chips with eDRAM?Michael S01/29/17 03:43 AM
                                            off die eDRAM?wumpus01/29/17 07:57 AM
                                              off die eDRAM?anon01/29/17 10:46 AM
                                      Sharing between servers and phonesrwessel01/27/17 11:36 PM
                                      Sharing between servers and phonesLinus Torvalds01/28/17 12:49 PM
                                        Sharing between servers and phonesrwessel01/29/17 09:56 PM
                                          Sharing between servers and phonesLinus Torvalds01/30/17 11:01 AM
                                            Sharing between servers and phonesrwessel01/31/17 01:29 AM
                                              Sharing between servers and phonesIreland01/31/17 08:55 AM
                                                Please keep your posts on topicDavid Kanter01/31/17 12:32 PM
                                                  Technology that can survive in harsh conditionsIreland01/31/17 01:51 PM
                                                    Stay on topic, you have been warnedDavid Kanter01/31/17 07:56 PM
                                                On topic summary and my thoughts on it. Jouni Osmala01/31/17 02:10 PM
                                                  On topic summary and my thoughts on it. Ireland01/31/17 02:27 PM
                                              Sharing between servers and phonesLinus Torvalds01/31/17 02:01 PM
                                                Sharing between servers and phonesLinus Torvalds01/31/17 02:49 PM
                                                  Sharing between servers and phonesDoug S01/31/17 03:12 PM
                                                Sharing between servers and phonesrwessel01/31/17 06:54 PM
                                                  Sharing between servers and phonesLinus Torvalds02/01/17 10:17 AM
                                                    Sharing between servers and phonesrwessel02/02/17 04:40 PM
                                                  Sharing between servers and phonesjoncmu02/01/17 02:36 PM
                                                    Sharing between servers and phonesChristian Borntraeger02/02/17 04:46 AM
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                      video renderingIreland01/24/17 06:26 PM
                      video renderingAaron Spink01/24/17 08:54 PM
                        video renderingRichardC01/25/17 05:26 AM
                          display bandwidthRichardC01/25/17 06:30 AM
                          video renderingIreland01/25/17 09:11 AM
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                              You can keep a coal furnace fed all the time.Ireland01/25/17 04:36 PM
                                You can keep a coal furnace fed all the time.anon01/27/17 04:29 AM
                                  You can keep a coal furnace fed all the time.Michael S01/27/17 08:22 AM
                                    You can keep a coal furnace fed all the time.Ireland01/27/17 11:59 AM
                                    You can keep a coal furnace fed all the time.anon01/27/17 04:09 PM
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                              video renderingIreland01/26/17 01:49 PM
                                video renderingIreland01/26/17 01:58 PM
                                video renderingRichardC01/26/17 04:24 PM
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                            video renderingIreland01/25/17 09:33 AM
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                            video renderingIreland01/25/17 04:26 PM
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                              cloud network infrastructureAaron Spink01/26/17 08:37 PM
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                  ARM-based supercomputersAaron Spink01/24/17 09:00 PM
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            ARM-based supercomputersRichardC01/23/17 07:57 AM
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    Mont blanc project and ARM HPC in generaljuanrga01/29/17 05:42 AM
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      Still idioticDavid Kanter01/30/17 08:49 AM
        Still idioticMr. Camel01/30/17 09:16 PM
        Still idioticjuanrga02/02/17 09:11 AM
      Mont blanc project and ARM HPC in generalIreland01/31/17 05:53 PM
        Four Things to Consider Ireland01/31/17 06:11 PM
          Four Things to Consider tarlinian01/31/17 07:38 PM
            Four Things to Consider Ireland01/31/17 07:58 PM
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                no evidence that it goes on a shipIreland02/02/17 02:57 PM
                  no evidence that it goes on a shipRichardC02/03/17 07:04 AM
                    no evidence that it goes on a shipIreland02/03/17 09:02 AM
              A better place to site a supercomputerAnon02/01/17 07:57 AM
                A better place to site a supercomputerIreland02/01/17 07:37 PM
                  A better Ireland..Anon02/01/17 08:52 PM
                    A better Ireland..slacker02/01/17 11:32 PM
                    A better Ireland..Ireland02/02/17 05:06 AM
                    He is manic (NT)anonymo02/02/17 01:21 PM
                      or a botanon02/02/17 03:17 PM
                        or a botanonymou502/02/17 04:46 PM
                        or a botnone02/02/17 11:45 PM
                          or a botanon02/03/17 10:30 AM
                        Better bot example: amanfrommars1Doug S02/03/17 11:44 AM
            Make allowances, the man never sleeps..Anon01/31/17 09:22 PM
        Mont blanc project and ARM HPC in generaletudiant02/02/17 09:39 AM
          Mont blanc project and ARM HPC in generalIreland02/02/17 12:12 PM
            Connection between two different modelsIreland02/02/17 12:18 PM
              Connection between two different modelsetudiant02/04/17 03:40 PM
                Connection between two different modelsRichardC02/06/17 09:36 AM
                  Connection between two different modelsdmcq02/06/17 11:07 AM
                  Connection between two different modelsIreland02/06/17 12:17 PM
                    probably not the right forum ...RichardC02/06/17 01:31 PM
                      probably not the right forum ...Ireland02/06/17 02:53 PM
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