Virtually tagged L1-caches

By: sr (, September 8, 2021 10:35 am
Room: Moderated Discussions
Hugo Décharnes ( on September 8, 2021 10:46 am wrote:
> You just repeated what I said, that is, VIVT is not the way to go.
> BTW, L2 access time is critical, and TLB coverage (not accuracy) does not compensate, in that most
> workload are bounded by the cache latency, not the TLB coverage. Yes, VIVPT enables to move TLB away
> from the time-critical load-return path, enabling bigger TLBs. But you must reduce the L2 hit latency
> as much as possible. We are talking about percents of performance for a typical big core.

Point for VIVT L1 is that there's zero need to burn power for TLB translation for L1 hit. Data already in cache can accessed and verified without need to translate address. As CPU core can do many L1-operations per cycle at least for L1-data TLB needs to be multiported, where instead L2 can service only one request per clock so single-ported TLB will be fine.

For that Power10 they document to have 8.5 cycle TLB translation and 13.5 clock cycle 2MB L2 access latency, so no difference to comparable Intel / AMD L2 latencies(12 512KB Zen3, 14 1.25MB Willow Cove). So either there's no additional L2 access penalty after L1 miss from TLB translation or Intel and AMD also does TLB translation only after L1 miss.

IBM is documented to have 64 slot fully associative ERAT with 4K TLB - that's pretty comparative to what AMD describes, 64 slot fully associative L1 TLB and 2K L2 TLB.....

Think about it, how energy-efficient would 64 way fully associative triple ported every cycle accessible TLB be? If someone has such a structure in their design getting rid of it would increase power-efficiency of design massively.....
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TopicPosted ByDate
POWER10 SAP SD benchmarkanon22021/09/06 02:36 PM
  POWER10 SAP SD benchmarkDaniel B2021/09/07 01:31 AM
    "Cores" (and SPEC)Rayla2021/09/07 06:51 AM
      "Cores" (and SPEC)anon2021/09/07 02:56 PM
  POWER10 SAP SD benchmarkAnon2021/09/07 02:24 PM
    POWER10 SAP SD benchmarkAnon2021/09/07 02:27 PM
  Virtually tagged L1-cachessr2021/09/08 04:49 AM
    Virtually tagged L1-cachesdmcq2021/09/08 07:22 AM
      Virtually tagged L1-cachessr2021/09/08 07:56 AM
      Virtually tagged L1-cachesHugo Décharnes2021/09/08 07:58 AM
        Virtually tagged L1-cachessr2021/09/08 09:09 AM
          Virtually tagged L1-cachesHugo Décharnes2021/09/08 09:46 AM
            Virtually tagged L1-cachessr2021/09/08 10:35 AM
              Virtually tagged L1-cachesHugo Décharnes2021/09/08 11:23 AM
                Virtually tagged L1-cachessr2021/09/08 11:40 AM
                  Virtually tagged L1-cachesanon2021/09/09 02:16 AM
                    Virtually tagged L1-cachesKonrad Schwarz2021/09/10 04:19 AM
                      Virtually tagged L1-cachesHugo Décharnes2021/09/10 05:59 AM
                        Virtually tagged L1-cachesanon2021/09/14 02:17 AM
                          Virtually tagged L1-cachesdmcq2021/09/14 08:34 AM
                            Or use a PLB (NT)Paul A. Clayton2021/09/14 08:45 AM
                              Or use a PLBLinus Torvalds2021/09/14 02:27 PM
                                Or use a PLBanon2021/09/14 11:15 PM
                                  Or use a PLBMichael S2021/09/15 02:21 AM
                                    Or use a PLBdmcq2021/09/15 02:42 PM
                                      Or use a PLBKonrad Schwarz2021/09/16 03:24 AM
                                        Or use a PLBMichael S2021/09/16 09:13 AM
                                          Or use a PLB---2021/09/16 12:02 PM
                                  PLB referencePaul A. Clayton2021/09/18 01:35 PM
                                    PLB referenceMichael S2021/09/18 03:14 PM
                                      Demand paging/translation orthogonalPaul A. Clayton2021/09/19 06:33 AM
                                        Demand paging/translation orthogonalMichael S2021/09/19 08:10 AM
                                      PLB referenceCarson2021/09/20 09:19 PM
                                    PLB referencesr2021/09/20 05:02 AM
                                      PLB referenceMichael S2021/09/20 06:03 AM
                                        PLB referenceLinus Torvalds2021/09/20 11:10 AM
                                  Or use a PLBsr2021/09/20 03:32 AM
                              Or use a PLBsr2021/09/21 08:36 AM
                                Or use a PLBLinus Torvalds2021/09/21 09:04 AM
                                  Or use a PLBsr2021/09/21 09:48 AM
                                    Or use a PLBLinus Torvalds2021/09/21 12:55 PM
                                      Or use a PLBsr2021/09/22 05:55 AM
                                        Or use a PLBrwessel2021/09/22 06:09 AM
                                        Or use a PLBLinus Torvalds2021/09/22 10:50 AM
                                          Or use a PLBsr2021/09/22 12:00 PM
                                            Or use a PLBdmcq2021/09/22 03:07 PM
                                            Or use a PLBEtienne Lorrain2021/09/23 07:50 AM
                                          Or use a PLBanon22021/09/22 03:09 PM
                                            Or use a PLBdmcq2021/09/23 01:35 AM
                                          Or use a PLB2021/09/23 08:37 AM
                                            Or use a PLBLinus Torvalds2021/09/23 11:01 AM
                                              Or use a PLBgpd2021/09/24 02:59 AM
                                                Or use a PLBLinus Torvalds2021/09/24 09:45 AM
                                                  Or use a PLBdmcq2021/09/24 11:43 AM
                                                  Or use a PLBsr2021/09/25 09:19 AM
                                                    Or use a PLBLinus Torvalds2021/09/25 09:44 AM
                                                      Or use a PLBsr2021/09/25 10:11 AM
                                                        Or use a PLBLinus Torvalds2021/09/25 10:31 AM
                                                          Or use a PLBsr2021/09/25 10:52 AM
                                                            Or use a PLBLinus Torvalds2021/09/25 11:05 AM
                                                              Or use a PLBsr2021/09/25 11:23 AM
                                                                Or use a PLBrwessel2021/09/25 02:29 PM
                                                                  Or use a PLBsr2021/09/30 11:22 PM
                                                                    Or use a PLBrwessel2021/10/01 05:19 AM
                                                                      Or use a PLBDavid Hess2021/10/01 09:35 AM
                                                                        Or use a PLBrwessel2021/10/02 03:47 AM
                                                                      Or use a PLBsr2021/10/02 10:16 AM
                                                                        Or use a PLBrwessel2021/10/02 10:53 AM
                                                          Or use a PLBLinus Torvalds2021/09/25 10:57 AM
                                                            Or use a PLBsr2021/09/25 11:07 AM
                                                              Or use a PLBLinus Torvalds2021/09/25 11:21 AM
                                                                Or use a PLBsr2021/09/25 11:40 AM
                                                                  Or use a PLBnksingh2021/09/27 08:07 AM
                                                          Or use a PLB2021/09/27 08:02 AM
                                                            Or use a PLBLinus Torvalds2021/09/27 09:20 AM
                                                              Or use a PLBLinus Torvalds2021/09/27 11:58 AM
                                                                Or use a PLBdmcq2021/09/28 09:59 AM
                                              Or use a PLBsr2021/09/25 09:34 AM
                                                Or use a PLBrwessel2021/09/25 02:44 PM
                                                  Or use a PLBsr2021/10/01 12:04 AM
                                                    Or use a PLBrwessel2021/10/01 05:33 AM
                                                      I386 segmentation highlightssr2021/10/04 06:53 AM
                                                        I386 segmentation highlightsAdrian2021/10/04 08:53 AM
                                                          I386 segmentation highlightssr2021/10/04 09:19 AM
                                                        I386 segmentation highlightsrwessel2021/10/04 03:57 PM
                                                          I386 segmentation highlightssr2021/10/05 10:16 AM
                                                            I386 segmentation highlightsMichael S2021/10/05 11:27 AM
                                                            I386 segmentation highlightsrwessel2021/10/05 03:20 PM
                                                Or use a PLBJohnG2021/09/25 09:18 PM
                                              Or use a PLB2021/09/27 06:37 AM
                                                Or use a PLBHeikki Kultala2021/09/28 02:53 AM
                                                  Or use a PLBrwessel2021/09/28 06:29 AM
                                        Or use a PLBDavid Hess2021/09/23 05:00 PM
                                          Or use a PLBAdrian2021/09/24 12:21 AM
                                            Or use a PLBdmcq2021/09/25 11:41 AM
                                        Or use a PLBblaine2021/09/26 10:19 PM
                                          Or use a PLBDavid Hess2021/09/27 10:35 AM
                                            Or use a PLBblaine2021/09/27 04:19 PM
                                            Or use a PLBAdrian2021/09/27 09:40 PM
                                              Or use a PLBAdrian2021/09/27 09:59 PM
                                                Or use a PLBdmcq2021/09/28 06:45 AM
                                              Or use a PLBrwessel2021/09/28 06:45 AM
                                              Or use a PLBDavid Hess2021/09/28 11:50 AM
                                                Or use a PLBEtienne Lorrain2021/09/30 12:25 AM
                                                  Or use a PLBDavid Hess2021/10/01 09:40 AM
                                  MMU privilegessr2021/09/21 10:07 AM
                                    MMU privilegesLinus Torvalds2021/09/21 12:49 PM
                            Virtually tagged L1-cachesKonrad Schwarz2021/09/16 03:18 AM
                          Virtually tagged L1-cachesCarson2021/09/16 12:12 PM
                            Virtually tagged L1-cachesanon22021/09/16 04:16 PM
                              Virtually tagged L1-cachesrwessel2021/09/16 05:29 PM
                          Virtually tagged L1-cachessr2021/09/20 03:20 AM
              Virtually tagged L1-caches---2021/09/08 01:28 PM
                Virtually tagged L1-cachesanonymou52021/09/08 07:28 PM
                  Virtually tagged L1-cachesanonymou52021/09/08 07:34 PM
                  Virtually tagged L1-caches---2021/09/09 09:14 AM
                    Virtually tagged L1-cachesanonymou52021/09/09 09:44 PM
                Multi-threading?David Kanter2021/09/09 08:32 PM
                  Multi-threading?---2021/09/10 08:19 AM
                Virtually tagged L1-cachessr2021/09/11 12:19 AM
                Virtually tagged L1-cachessr2021/09/11 12:36 AM
                  Virtually tagged L1-caches---2021/09/11 08:53 AM
                    Virtually tagged L1-cachessr2021/09/11 11:43 PM
                      Virtually tagged L1-cachesLinus Torvalds2021/09/12 10:10 AM
                        Virtually tagged L1-cachessr2021/09/12 10:57 AM
                          Virtually tagged L1-cachesdmcq2021/09/13 07:31 AM
                            Virtually tagged L1-cachessr2021/09/20 03:11 AM
            Virtually tagged L1-cachessr2021/09/11 01:49 AM
      Virtually tagged L1-cachesLinus Torvalds2021/09/08 11:34 AM
        Virtually tagged L1-cachesdmcq2021/09/09 01:46 AM
          Virtually tagged L1-cachesdmcq2021/09/09 01:58 AM
          Virtually tagged L1-cachessr2021/09/11 12:29 AM
            Virtually tagged L1-cachesdmcq2021/09/11 07:59 AM
              Virtually tagged L1-cachessr2021/09/11 11:57 PM
                Virtually tagged L1-cachesdmcq2021/09/12 07:44 AM
                  Virtually tagged L1-cachessr2021/09/12 08:48 AM
                    Virtually tagged L1-cachesdmcq2021/09/12 12:22 PM
                      Virtually tagged L1-cachessr2021/09/20 03:40 AM
    Where do you see this information? (NT)anon22021/09/09 01:45 AM
      Where do you see this information?sr2021/09/11 12:40 AM
        Where do you see this information?anon22021/09/11 12:53 AM
          Where do you see this information?sr2021/09/11 01:08 AM
            Thank you (NT)anon22021/09/11 03:31 PM
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