transactional memory = memory lock/unlock

By: sr (nobody.delete@this.nowhere.com), April 10, 2021 12:56 am
Room: Moderated Discussions
Linus Torvalds (torvalds.delete@this.linux-foundation.org) on April 7, 2021 10:35 am wrote:

> No.
>
> Transactional memory doesn't make locking easier. Not at all.
>
> Transactional memory makes locking much harder. It adds a lot of new cases, it
> adds all that fallback logic, and it adds a huge number of debugging problems.

Let's start from basics. I can't be only one that have been wondering why there isn't lock/unlock instruction for shared memory regions? It should be there so it could be always used instead of software locking, which is always hard to implement and debug.

It isn't there because it's a little hard to implement in hardware.


But it can be done.

For quick look at TSX it seems to exist to provide starting point for software development and provide quite good evolving path for hardware.


As fallback logic - it's just the evil that needs to be there with current hardware implementation. To provide forward progress they need to provide unlimited memory for transactions. To make it happen it needs both OS and hardware support to being able spill transactions to memory - and for hardware implementation that probably would be too costly now as most of benchmarked software won't make any use of transactions.

And about that big transactions are more probably of aborting - of course big transactions are chopped to smaller ones. In closed nesting parent transaction is safe from child transaction aborts if harware supports(TSX now support closed nesting but aborts always everything from beginning of first transaction at current harware implementation) and in open nesting parent transaction can commit without child transactions - that isn't supported in TSX yet.



But in the end if you got some functional transaction memory to operate with you could lock memory in fine-grained fashion where hardware does hard part - for most part deadlocks and other unwanted memory lock problems just go away because locking is done in hardware instead of software.

But using transactional memory just for lock elision where all hard work is done already for locking and just except higher performance because of opportunistic execution of traditional software locking is a bit disparaging attitude towards tranactional memory possibilities.


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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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