CMPXCHG latency

By: Zan (zan.delete@this.hate.spam.net), April 2, 2008 12:11 am
Room: Moderated Discussions
Just caught a glimpse of what you are probably driving at. Given the common idioms in your example,

>
>spinlock(lock);
>list_add(entry, list);
>list->count++;
>spinunlock(lock);
>

What's needed from the atomic instruction in the spinlock() function is obviously some kind memory barrier semantics. In a safe but slow implementation you can flush all the pipelines and L/S buffers, then do a bus transaction to make sure you have local cache line in exclusive state. But in the uncontended common case, it's too wasteful for an OoO core.

Are you proposing to speculate past the atomic instruction and borrow a little bit from transaction memory? It's really plausible to speculate ahead and only abort when the local cache line which contains the atomic variable is not in exclusive state. If it can be done, it'll be a huge boost to lock performance in the common case.

Have you thought about bouncing your idea with Intel people. You guys are all in Hillsboro, right?
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
Nehalem Architecture: Improvements Detailed Blut Aus Nord2008/03/17 02:52 PM
  Nehalem Architecture: Improvements Detailed bah2008/03/17 04:45 PM
    Nehalem Architecture: Improvements Detailed Linus Torvalds2008/03/17 06:14 PM
      Nehalem Architecture: Improvements Detailed Gabriele Svelto2008/03/18 01:11 AM
        Nehalem Architecture: Improvements Detailed Henrik S2008/03/18 04:23 AM
        Nehalem Architecture: Improvements Detailed Doug Siebert2008/03/18 09:48 PM
          Nehalem Architecture: Improvements Detailed anon2008/03/18 10:37 PM
            Nehalem Architecture: Improvements Detailed Doug Siebert2008/03/19 05:23 PM
          Nehalem Architecture: Improvements Detailed Ian Ollmann2008/03/19 08:15 AM
            SSE 4.2 Michael S2008/03/19 04:13 PM
              SSE 4.2 Ian Ollmann2008/03/20 09:56 AM
              SSE 4.2 anonymous2008/03/20 12:29 PM
                SSE 4.2 David W. Hess2008/03/21 07:24 AM
                  SSE 4.2 anonymous2008/03/22 07:27 AM
      CMPXCHG latencyDavid Kanter2008/03/28 05:59 PM
        CMPXCHG latencyanonymous coward2008/03/28 10:24 PM
          CMPXCHG latencyDavid Kanter2008/03/28 10:26 PM
            CMPXCHG latencyLinus Torvalds2008/03/29 11:43 AM
              CMPXCHG latencyDavid W. Hess2008/03/29 11:56 AM
              CMPXCHG latencyLinus Torvalds2008/03/29 02:17 PM
                CMPXCHG latencyGabriele Svelto2008/03/31 12:25 AM
                  CMPXCHG latencyMichael S2008/03/31 12:38 AM
                    CMPXCHG latencynick2008/03/31 12:52 AM
                      CMPXCHG latencyMichael S2008/03/31 01:51 AM
                        CMPXCHG latencyGabriele Svelto2008/03/31 02:08 AM
                        CMPXCHG latencynick2008/03/31 07:20 PM
                          CMPXCHG latencyMichael S2008/04/01 01:14 AM
                            CMPXCHG latencynick2008/04/01 02:34 AM
                    CMPXCHG latencyLinus Torvalds2008/03/31 10:16 AM
                      CMPXCHG latencyAaron Spink2008/03/31 07:15 PM
                        CMPXCHG latencynick2008/03/31 07:34 PM
                        CMPXCHG latencyLinus Torvalds2008/04/01 08:25 AM
                          CMPXCHG latencyZan2008/04/01 09:54 PM
                          CMPXCHG latencyZan2008/04/02 12:11 AM
                            CMPXCHG latencyLinus Torvalds2008/04/02 08:04 AM
                              CMPXCHG latencyZan2008/04/02 11:02 AM
                                CMPXCHG latencyLinus Torvalds2008/04/02 12:02 PM
                                  CMPXCHG latencyZan2008/04/02 04:15 PM
                      CMPXCHG latencyMichael S2008/04/01 01:26 AM
                        CMPXCHG latencyLinus Torvalds2008/04/01 07:08 AM
                CMPXCHG latency - Intel sourceWouter Tinus2008/04/02 12:36 PM
                  CMPXCHG latency - Intel sourceLinus Torvalds2008/04/02 02:21 PM
                    CMPXCHG latency - Intel sourceDavid Kanter2008/04/02 02:39 PM
    Nehalem Architecture: Improvements Detailed Philip Honermann2008/03/19 01:11 PM
      Nehalem Architecture: Improvements Detailed Linus Torvalds2008/03/19 01:43 PM
        CMPXCHG - all or nothingMichael S2008/03/19 03:49 PM
          multithreading - all or nothingno@thanks.com2008/03/19 05:17 PM
          CMPXCHG - all or nothingLinus Torvalds2008/03/19 05:21 PM
            CMPXCHG - all or nothingMichael S2008/03/20 06:38 AM
              CMPXCHG - all or nothingLinus Torvalds2008/03/20 08:45 AM
                CMPXCHG - all or nothingMichael S2008/03/21 07:08 AM
                  CMPXCHG - all or nothingLinus Torvalds2008/03/21 08:47 AM
            CMPXCHG - all or nothingHenrik S2008/03/20 10:09 AM
              CMPXCHG - all or nothingLinus Torvalds2008/03/20 10:53 AM
                CMPXCHG - all or nothingHenrik S2008/03/20 12:03 PM
                  CMPXCHG - all or nothingLinus Torvalds2008/03/20 01:12 PM
                    CMPXCHG - all or nothingHenrik S2008/03/21 12:13 AM
                      CMPXCHG - all or nothingGabriele Svelto2008/03/21 01:22 AM
        Nehalem Architecture: Improvements Detailed Philip Honermann2008/03/19 06:28 PM
          Nehalem Architecture: Improvements Detailed Linus Torvalds2008/03/19 07:42 PM
            Nehalem Architecture: Improvements Detailed Philip Honermann2008/03/20 06:03 PM
              Nehalem Architecture: Improvements Detailed Linus Torvalds2008/03/20 06:33 PM
                Nehalem Architecture: Improvements Detailed Philip Honermann2008/03/25 06:37 AM
                  Nehalem Architecture: Improvements Detailed Linus Torvalds2008/03/25 08:52 AM
                    What is DCAS? (NT)David Kanter2008/03/25 10:13 AM
                      Double compare-and-exchangeHenrik S2008/03/25 10:57 AM
                        Double compare-and-exchangeLinus Torvalds2008/03/25 11:38 AM
                          Double compare-and-exchangesavantu2008/03/25 01:54 PM
                            Double compare-and-exchangeLinus Torvalds2008/03/25 04:09 PM
                              Double compare-and-exchangeJamie Lucier2008/03/25 08:55 PM
                                Double compare-and-exchangesavantu2008/03/25 09:15 PM
                                  Double compare-and-exchangeHenrik S2008/03/26 08:40 AM
                                    Double compare-and-exchangeArun Ramakrishnan2008/03/27 02:07 AM
                                      Double compare-and-exchangeHenrik S2008/03/27 04:45 AM
                                  Surely GPL applies ?Richard Cownie2008/03/26 10:05 AM
                                    Surely GPL applies ?anon2008/03/26 02:58 PM
                                    Surely GPL applies ?Paul2008/03/26 05:01 PM
                                Double compare-and-exchangesomeone2008/03/25 09:18 PM
                                  Double compare-and-exchangeArun Ramakrishnan2008/03/27 02:03 AM
                                    Double compare-and-exchangesavantu2008/03/27 03:01 AM
                                      Double compare-and-exchangeArun Ramakrishnan2008/03/30 09:09 AM
                                        Double compare-and-exchangesavantu2008/03/30 09:59 AM
                                Double compare-and-exchangeLinus Torvalds2008/03/26 10:50 AM
                                  Double compare-and-exchangeanon2008/03/26 04:47 PM
                                  Double compare-and-exchangePaul2008/03/26 05:07 PM
                          Double compare-and-exchangeHoward Chu2008/03/25 05:18 PM
  Nehalem Architecture: Improvements Detailed Mr. Camel2008/03/17 08:50 PM
    Nehalem Architecture: Improvements Detailed anonymous2008/03/17 09:20 PM
  TFP will finally come :-)Paul A. Clayton2008/03/18 12:56 PM
  Nehalem Architecture: Improvements Detailed IntelUser20002008/03/27 07:46 PM
    Nehalem Architecture: Improvements Detailed David Kanter2008/03/27 10:21 PM
      Nehalem Architecture: Improvements Detailed nick2008/03/27 11:06 PM
        Nehalem Architecture: Improvements Detailed David Kanter2008/03/28 02:45 PM
          Nehalem Architecture: Improvements Detailed nick2008/03/28 07:52 PM
  L1 I-cachepuzzled2008/04/01 07:53 AM
    L1 I-cacheS. Rao2008/04/01 09:47 AM
    L1 I-cacherwessel2008/04/01 12:23 PM
    L1 I-cacheGabriele Svelto2008/04/03 12:30 AM
Reply to this Topic
Name:
Email:
Topic:
Body: No Text
How do you spell tangerine? 🍊