IBM zArch TM - guaranteed progress

By: David Kanter (dkanter.delete@this.realworldtech.com), March 31, 2021 8:37 pm
Room: Moderated Discussions
Linus Torvalds (torvalds.delete@this.linux-foundation.org) on March 31, 2021 4:44 pm wrote:

> With the constrained version, you also don't end up needing the "transaction predictor"
> logic that I personally am convinced is required for the generic lock elision case.
>
> That said, I have this dim memory of the zSeries retry mode being "go very very slow". So I don't know
> how well it works in practice if you actually have conflicts. Again, I haven't actually used the zSeries
> version, but I can very much believe that the constrained TM model is very useful in specialized libraries
> and/or for people who have some very hot and simple case they can code specially for it.

The zArch version of HTM does have forward progress guarantees. However, to deliver those guarantees, the CPU can do all sorts of fun things during fallback - e.g., reducing issue width down to 1 instruction, disabling out-of-order execution, etc.

So it will make forward progress, but it could be slow!

> And all the transactional memory models - including the constrained version - have a fundamental issue with debugging
> and things like single-stepping. But admittedly so does load-locked / store-conditional, and it hasn't been a
> huge issue. Again, the issue is much less in the constrained model than it is in the general case.
>
> But at the same time it obviously isn't that holy grail of big lock elision to make it easy
> to write scalable threaded software. Which nobody has actually really gotten to work.

Yes, I'm also a bit sad and disappointed. I think one real problem is that your speculative regions become quite large and expensive to rollback. Also, many workloads do have frequent interrupts, etc.

David
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TopicPosted ByDate
Armv9 officially announcedJon Masters2021/03/30 11:41 AM
  Armv9 officially announcedGabriele Svelto2021/03/30 01:27 PM
    HTM and TLEFoo_2021/03/30 01:31 PM
      HTM and TLEdmcq2021/03/30 03:03 PM
      Intel RTM and HLE is a successGanon2021/03/30 05:22 PM
        Intel RTM and HLE is a success (is it?)Foo_2021/03/31 01:16 AM
          Intel RTM and HLE was an abject failureanonymou52021/03/31 03:04 AM
          Intel RTM and HLE is a success (is it?)Andrey2021/03/31 05:27 AM
            Intel RTM and HLE is a success (is it?)Foo_2021/03/31 05:58 AM
              Intel RTM and HLE is a success (is it?)Andrey2021/03/31 07:45 AM
                Intel RTM and HLE is a success (is it?)Foo_2021/03/31 09:32 AM
                  Intel RTM and HLE is a success (is it?)Andrey2021/03/31 09:57 AM
                    Intel RTM and HLE is a success (is it?)anonymou52021/03/31 10:39 AM
                      ^ feel free to delete this one -- broken HTML there (NT)anonymou52021/03/31 10:40 AM
                      Intel RTM and HLE is a success (is it?)Andrey2021/03/31 10:47 AM
                    Intel RTM and HLE is a success (is it?)anonymou52021/03/31 10:40 AM
                Intel RTM and HLE is a success (is it?)Ganon2021/03/31 09:58 AM
                  Intel RTM and HLE is a success (is it?)anonymou52021/03/31 10:42 AM
                  Intel RTM and HLE is a success (is it?)Linus Torvalds2021/03/31 11:54 AM
                    Intel RTM and HLE is a success (is it?)Linus Torvalds2021/03/31 12:00 PM
                      Any idea about IBM?Mark Roulo2021/03/31 12:15 PM
                        Any idea about IBM?Linus Torvalds2021/03/31 12:37 PM
                          Any idea about IBM?dmcq2021/03/31 03:04 PM
                            Any idea about IBM?Linus Torvalds2021/03/31 04:44 PM
                              A non straw man view of hardware transactional memoryGanon2021/03/31 07:52 PM
                                A non straw man view of hardware transactional memoryanon22021/03/31 11:03 PM
                                  A non straw man view of hardware transactional memoryCarson2021/04/02 01:11 AM
                                    A non straw man view of hardware transactional memoryanon22021/04/02 05:28 AM
                              IBM zArch TM - guaranteed progressDavid Kanter2021/03/31 08:37 PM
                              Any idea about IBM?Andrey2021/03/31 11:31 PM
                                Any idea about IBM?Linus Torvalds2021/04/01 10:54 AM
                                  Any idea about IBM?Andrey2021/04/02 12:50 PM
                        Any idea about IBM?someone2021/04/01 12:02 AM
                      Intel RTM and HLE is a success (is it?)anon22021/03/31 03:46 PM
                        Intel RTM and HLE is a success (is it?)Linus Torvalds2021/03/31 05:08 PM
                          Leaving it to software is tricky!David Kanter2021/03/31 08:41 PM
                            And a hardware predicttor needs access to fallback timingCarson2021/04/01 11:13 PM
                              Hardware fallback pathAnon2021/04/02 10:51 AM
                              And a hardware predicttor needs access to fallback timingLinus Torvalds2021/04/03 10:41 AM
                                And a hardware predicttor needs access to fallback timingLinus Torvalds2021/04/03 11:11 AM
                                  And a hardware predicttor needs access to fallback timingsr2021/04/03 11:30 AM
                                    And a hardware predicttor needs access to fallback timingLinus Torvalds2021/04/03 12:14 PM
                                      And a hardware predicttor needs access to fallback timingsr2021/04/03 12:39 PM
                                        And a hardware predicttor needs access to fallback timingAnon2021/04/03 02:08 PM
                                          And a hardware predicttor needs access to fallback timingsr2021/04/03 02:33 PM
                                            And a hardware predicttor needs access to fallback timingdmcq2021/04/04 05:35 AM
                                        And a hardware predicttor needs access to fallback timingLinus Torvalds2021/04/03 02:22 PM
                                          Transactional memory isn't exclusive to lockingsr2021/04/04 12:17 AM
                                            Transactional memory isn't exclusive to lockingAspect of Anonimity2021/04/04 03:49 AM
                                            Transactional memory isn't exclusive to lockingAndrey2021/04/04 04:58 AM
                                              Transactional memory isn't exclusive to lockingsr2021/04/04 10:10 AM
                                                Transactional memory isn't exclusive to lockingAndrey2021/04/04 10:33 AM
                                                  Transactional memory isn't exclusive to lockingsr2021/04/05 02:41 AM
                                      And a hardware predicttor needs access to fallback timingGeertB2021/04/04 07:08 PM
                            Leaving it to software is tricky!Andrey2021/04/02 03:00 PM
                          Intel RTM and HLE is a success (is it?)@never_released2021/04/01 08:21 AM
                            Intel RTM and HLE is a success (is it?)@never_released2021/04/01 08:30 AM
                            Intel RTM and HLE is a success (is it?)Linus Torvalds2021/04/01 10:00 AM
                              Intel RTM and HLE is a success (is it?)dmcq2021/04/01 10:35 AM
                                Intel RTM and HLE is a success (is it?)Linus Torvalds2021/04/01 10:59 AM
                                  Is HTM actually in ARMv9?dncq2021/04/01 11:26 AM
                                    Is HTM actually in ARMv9?Linus Torvalds2021/04/01 12:13 PM
                              Intel RTM and HLE is a success (is it?)Jörn Engel2021/04/01 09:15 PM
                          Intel RTM and HLE is a success (is it?)---2021/04/02 10:00 AM
                      Intel RTM and HLE is a success (is it?)Jon Masters2021/04/01 10:56 AM
                        RockMichael S2021/04/01 12:29 PM
            Intel RTM and HLE is a success (is it?)Linus Torvalds2021/03/31 11:50 AM
              Intel RTM and HLE is a success (is it?)anon22021/03/31 03:57 PM
                Intel RTM and HLE is a success (is it?)anon32021/03/31 04:09 PM
          Intel RTM and HLE is a success (is it?)someone2021/03/31 11:56 PM
            Intel RTM and HLE is a success (is it?)someone2021/04/01 12:21 AM
              Intel RTM and HLE is a success (is it?)none2021/04/01 04:31 AM
                Intel RTM and HLE is a success (is it?)anonymou52021/04/01 09:24 AM
                  Intel RTM and HLE is a success (is it?)anony2021/04/01 10:26 AM
                  Intel RTM and HLE is a success (is it?)none2021/04/01 11:20 AM
                Intel RTM and HLE is a success (is it?)Brendan2021/04/01 05:23 PM
                  Intel RTM and HLE is a success (is it?)Adrian2021/04/02 01:03 AM
      Transactional memory similarity to garbage collectionPaul A. Clayton2021/04/05 01:53 PM
        Maybe notMark Roulo2021/04/05 03:07 PM
        Transactional memory similarity to garbage collectionAnon2021/04/05 03:14 PM
        No conflict between theory and practiceAspect of Anonimity2021/04/05 07:57 PM
          No conflict between theory and practiceNoSpammer2021/04/05 09:38 PM
            No conflict between theory and practicedmcq2021/04/06 07:05 AM
              No conflict between theory and practicesr2021/04/06 09:22 AM
                No conflict between theory and practiceBen LaHaise2021/04/06 03:43 PM
                  No conflict between theory and practicesr2021/04/07 09:42 AM
                    No conflict between theory and practiceAnon2021/04/07 10:06 AM
                    No conflict between theory and practiceLinus Torvalds2021/04/07 10:35 AM
                      No conflict between theory and practicesr2021/04/07 12:34 PM
                        If HTM were well implemented, nobody would complain (NT)Anon2021/04/07 12:54 PM
                          If HTM were well implemented, nobody would complaindmcq2021/04/07 03:36 PM
                            If HTM were well implemented, nobody would complainAnon2021/04/07 04:04 PM
                          If HTM were well implemented, nobody would complain---2021/04/08 09:37 AM
                        No conflict between theory and practiceLinus Torvalds2021/04/07 01:20 PM
                          No conflict between theory and practiceAndrey2021/04/07 02:32 PM
                            No conflict between theory and practicedmcq2021/04/07 03:32 PM
                              No conflict between theory and practiceanonymou52021/04/07 04:26 PM
                              No conflict between theory and practiceAndrey2021/04/07 05:54 PM
                                No conflict between theory and practiceLinus Torvalds2021/04/08 08:41 AM
                                  No conflict between theory and practiceAndrey2021/04/08 09:12 AM
                                  No conflict between theory and practiceRobert Williams2021/04/08 09:15 AM
                                    No conflict between theory and practiceLinus Torvalds2021/04/08 09:56 AM
                                      No conflict between theory and practiceRobert Williams2021/04/08 07:50 PM
                                        No conflict between theory and practiceLinus Torvalds2021/04/09 09:25 AM
                                          TSX for all?Robert Williams2021/04/09 12:46 PM
                                            It helps adoption when developers can run the code an their machines.Mark Roulo2021/04/09 12:54 PM
                                              It helps adoption when developers can run the code an their machines.me2021/04/09 02:21 PM
                                                It helps adoption when developers can run the code an their machines.Andrey2021/04/10 07:08 AM
                                                  It helps adoption when developers can run the code an their machines.me2021/04/10 12:43 PM
                                                    It helps adoption when developers can run the code an their machines.Robert Williams2021/04/10 07:05 PM
                                                      It helps adoption when developers can run the code an their machines.Andrey2021/04/11 01:42 AM
                                                        It helps adoption when developers can run the code an their machines.Michael S2021/04/11 04:23 AM
                                              It helps adoption when developers can run the code an their machines.Robert Williams2021/04/10 08:24 AM
                                                It helps adoption when developers can run the code an their machines.Andrey2021/04/10 10:36 AM
                                                  It helps adoption when developers can run the code an their machines.Michael S2021/04/10 10:58 AM
                                                    It helps adoption when developers can run the code an their machines.Robert Williams2021/04/10 11:42 AM
                                                    It helps adoption when developers can run the code an their machines.Brendan2021/04/10 11:27 PM
                                                      It helps adoption when developers can run the code an their machines.Michael S2021/04/11 03:34 AM
                                                        It helps adoption when developers can run the code an their machines.Brendan2021/04/11 04:18 PM
                                            TSX for all?wumpus2021/04/09 01:10 PM
                                            TSX for all?Linus Torvalds2021/04/09 03:03 PM
                                              [CLICK BAIT?] Torvalds to recommend arm64!anonymous22021/04/09 03:17 PM
                                              TSX for all?Linus Torvalds2021/04/09 03:22 PM
                                                amen! (NT)anonymou52021/04/09 05:42 PM
                                            TSX for all?Emil Briggs2021/04/10 05:52 AM
                                              TSX for all?Michael S2021/04/10 11:13 AM
                                                TSX for all?Brendan2021/04/10 11:05 PM
                                          No conflict between theory and practiceanonymouse2021/04/09 03:02 PM
                            No conflict between theory and practiceLinus Torvalds2021/04/07 05:12 PM
                              No conflict between theory and practiceAndrey2021/04/07 05:33 PM
                                No conflict between theory and practiceanon22021/04/07 08:12 PM
                                  No conflict between theory and practiceAndrey2021/04/08 12:29 AM
                                    No conflict between theory and practiceAnon2021/04/08 12:50 AM
                                    No conflict between theory and practiceanon22021/04/08 12:52 AM
                                      No conflict between theory and practiceAndrey2021/04/08 02:41 AM
                                        No conflict between theory and practiceAdrian2021/04/08 03:09 AM
                                          No conflict between theory and practiceAndrey2021/04/08 03:50 AM
                                            No conflict between theory and practiceAdrian2021/04/08 05:07 AM
                                            No conflict between theory and practiceanon22021/04/08 05:18 AM
                                              No conflict between theory and practiceAndrey2021/04/08 08:18 AM
                                                No conflict between theory and practiceanon22021/04/08 09:11 AM
                                                  No conflict between theory and practiceAndrey2021/04/08 09:48 AM
                                                    No conflict between theory and practiceanon22021/04/08 04:10 PM
                                            No conflict between theory and practice---2021/04/08 08:30 PM
                                              No conflict between theory and practicedmcq2021/04/09 02:25 AM
                                                No conflict between theory and practiceLinus Torvalds2021/04/09 09:44 AM
                                        No conflict between theory and practiceanon22021/04/08 04:09 AM
                                          No conflict between theory and practicesr2021/04/10 01:22 AM
                                            No conflict between theory and practiceAnon2021/04/10 04:00 AM
                                              No conflict between theory and practiceEtienne Lorrain2021/04/12 12:56 AM
                                                No conflict between theory and practiceAnon2021/04/12 01:54 AM
                                                  No conflict between theory and practicedmcq2021/04/12 01:44 PM
                              No conflict between theory and practiceGabriele Svelto2021/04/08 01:03 AM
                                No conflict between theory and practicedmcq2021/04/12 01:53 PM
                                  No conflict between theory and practicedmcq2021/04/14 04:50 AM
                      transactional memory = memory lock/unlocksr2021/04/10 12:56 AM
                        transactional memory = memory lock/unlockAnon2021/04/10 04:05 AM
                    No conflict between theory and practiceanon22021/04/07 05:19 PM
                No conflict between theory and practicedmcq2021/04/07 01:16 PM
            No conflict between theory and practiceAnon2021/04/06 10:46 AM
            No conflict between theory and practiceAspect of Anonimity2021/04/06 02:16 PM
              No conflict between theory and practiceNoSpammer2021/04/10 12:02 AM
                No conflict between theory and practicesr2021/04/10 01:47 AM
                No conflict between theory and practiceAspect of Anonimity2021/04/10 11:30 PM
                  No conflict between theory and practiceAndrey2021/04/11 05:05 AM
                    HmAspect of Anonimity2021/04/12 07:29 PM
                      Special internal SRAM to store Mutex?Etienne Lorrain2021/04/13 01:01 AM
                        Special internal SRAM to store Mutex?Anon2021/04/13 01:26 AM
                        Special internal SRAM to store Mutex?Linus Torvalds2021/04/13 09:53 AM
                        Special internal SRAM to store Mutex?Dan Fay2021/04/13 12:03 PM
                          Special internal SRAM to store Mutex?Ben LaHaise2021/04/13 03:32 PM
                          Special internal SRAM to store Mutex?Gabriele Svelto2021/04/13 11:43 PM
                        Special internal SRAM to store Mutex?Carson2021/04/13 10:19 PM
          No conflict between theory and practicesr2021/04/06 07:12 AM
            No conflict between theory and practiceAnon2021/04/06 10:43 AM
            No conflict between theory and practiceAspect of Anonimity2021/04/06 03:20 PM
              No conflict between theory and practicesr2021/04/07 10:09 AM
                No conflict between theory and practiceanon22021/04/07 08:53 PM
  Armv9 officially announceddmcq2021/03/30 03:28 PM
    Totally backwads logic on compatibilityHeikki Kultala2021/03/30 03:44 PM
      Totally backwads logic on compatibilityDoug S2021/03/31 12:09 PM
        Totally backwads logic on compatibilitydmcq2021/03/31 03:15 PM
  Armv9 officially announcedv92021/04/12 03:57 PM
    Armv9 officially announcedj2021/04/13 05:07 AM
      Armv9 officially announcedDoug S2021/04/13 10:21 AM
        Armv9 officially announcedanonymou52021/04/13 11:06 AM
          Armv9 officially announcedDoug S2021/04/13 01:01 PM
        Armv9 officially announceddmcq2021/04/13 03:20 PM
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