Branch/jump target prediction -8

By: Simon Farnsworth (simon.delete@this.farnz.org.uk), August 19, 2016 3:17 am
Room: Moderated Discussions
Etienne (etienne_lorrain.delete@this.yahoo.fr) on August 19, 2016 1:25 am wrote:
> Maynard Handley (name99.delete@this.name99.org) on August 18, 2016 10:02 am wrote:
> > What provides more value is fixing the remaining problems
> > in this fetch pipeline. These might include things like
>
> Wouldn't it be worthwhile, because it seems technology has reach a point where fetching
> those "unit of code" (i.e. assembly instructions) very optimised, to make more work
> in each "unit of code" (so they can take more time to do more usefull stuff).
> Obviously it would not be with the same assembly instruction set, but if you had integer operations
> with saturation (could also be programmable saturation at for instance [0..4095]), integer division
> with round-up, round-down and round nearest - then the compiler would not need to generate so many
> simple assembly instructions with so many jumps, which seems so difficult to fetch.
>
> Also, if I may, more general question (obviously I am not
> in a domain when out-of-order execution is the rule):
> Nowadays on standard/personal computers, which kind of OOO level is available,
> how may assembly instructions can be waiting in the dispatcher?

http://www.realworldtech.com/haswell-cpu/3/ says that Haswell's OOO scheduling window is around 300 operations, based on a ROB of 192 µops, but Haswell being able to fuse µops before they enter the OOO engine.

The exact window depends on your instruction mix, but hundreds of instructions is the scale you're looking at on a modern desktop or server processor.

I'm not entirely clear on what code constructs to avoid with OOO, beyond the obvious of keeping your dependency chains under control - OOO can't help you if, within the OOO window, it can't find enough µops to execute. OTOH, compilers are now pretty good at helping you out here, so...
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TopicPosted ByDate
Branch/jump target predictionTravis2016/08/09 09:44 AM
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    Early decode of unconditional jumpsExophase2016/08/09 12:29 PM
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                Branch/jump target predictionGabriele Svelto2016/08/14 01:09 PM
            Just a thoughtAnon2016/08/14 09:40 AM
              Just a thought2016/08/16 05:58 AM
                Just a thoughtAnon2016/08/16 07:45 AM
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              Branch/jump target prediction2016/08/16 05:40 AM
                Branch/jump target predictionRicardo B2016/08/16 06:39 AM
                  Branch/jump target prediction -82016/08/16 08:23 AM
                    Branch/jump target prediction -8anon2016/08/16 09:09 AM
                    Branch/jump target prediction -8Ricardo B2016/08/16 09:33 AM
                      Branch/jump target prediction -8Exophase2016/08/16 10:02 AM
                        Branch/jump target prediction -8Ricardo B2016/08/16 10:31 AM
                        SPU hbr instruction (hint for branch)vvid2016/08/16 11:31 AM
                        Branch/jump target prediction -8no name2016/08/17 07:16 AM
                    Branch/jump target prediction -8Gabriele Svelto2016/08/16 10:46 AM
                      Branch/jump target prediction -8Etienne2016/08/17 12:27 AM
                        Branch/jump target prediction -8Gabriele Svelto2016/08/17 02:52 AM
                    Branch/jump target prediction -8Maynard Handley2016/08/18 09:02 AM
                      Branch/jump target prediction -82016/08/18 05:21 PM
                        Branch/jump target prediction -8Maynard Handley2016/08/18 06:27 PM
                          Branch/jump target prediction -8Megol2016/08/19 03:29 AM
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                        Atom, you're such a comedian.Jim Trent2016/08/18 09:39 PM
                          Atom, you're such a comedian.2016/08/19 02:23 AM
                      Branch/jump target prediction -8Etienne2016/08/19 12:25 AM
                        Branch/jump target prediction -8Simon Farnsworth2016/08/19 03:17 AM
                          Branch/jump target prediction -8Michael S2016/08/19 05:39 AM
                          Branch/jump target prediction -8anon2016/08/19 06:29 AM
                            Branch/jump target prediction -8Simon Farnsworth2016/08/19 07:34 AM
                              Branch/jump target prediction -8anon2016/08/19 07:48 AM
                                Branch/jump target prediction -8Exophase2016/08/19 10:03 AM
                                Branch/jump target prediction -8Maynard Handley2016/08/19 10:34 AM
                            Branch/jump target prediction -8David Kanter2016/08/19 11:23 PM
                        Branch/jump target prediction -8Ricardo B2016/08/19 06:18 AM
                          Branch/jump target prediction -8Maynard Handley2016/08/19 07:41 AM
                            Branch/jump target prediction -8Michael S2016/08/19 08:26 AM
                              Branch/jump target prediction -8Maynard Handley2016/08/19 12:47 PM
                                Branch/jump target prediction -8Michael S2016/08/21 12:53 AM
                                  Branch/jump target prediction -8Ricardo B2016/08/22 04:17 AM
                                    Branch/jump target prediction -8Michael S2016/08/22 04:58 AM
                                      Branch/jump target prediction -8Ricardo B2016/08/22 06:50 AM
                            Branch/jump target prediction -8Simon Farnsworth2016/08/19 08:28 AM
                              Branch/jump target prediction -8Simon Farnsworth2016/08/19 08:40 AM
                            Branch/jump target prediction -8David Kanter2016/08/22 11:05 PM
                              Branch/jump target prediction -8Maynard Handley2016/08/23 06:49 AM
                      Branch/jump target prediction -8anon2016/08/26 07:00 AM
                        Branch/jump target prediction -8anon2016/08/26 07:14 AM
                Branch/jump target predictionMegol2016/08/19 03:23 AM
          Branch/jump target predictionMegol2016/08/19 06:42 AM
            Branch/jump target predictionMaynard Handley2016/08/19 10:46 AM
              Branch/jump target predictionDavid Kanter2016/08/19 11:34 PM
                Branch/jump target predictionMaynard Handley2016/08/20 06:07 AM
            Branch/jump target predictionsylt2016/08/19 10:48 AM
              Branch/jump target predictionsylt2016/08/19 11:00 AM
              Branch/jump target predictionMegol2016/08/21 09:27 AM
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                  The (apparent) state of trace caches on modern CPUsExophase2016/08/22 07:55 PM
                    The (apparent) state of trace caches on modern CPUsanon2016/08/22 11:36 PM
                      The (apparent) state of trace caches on modern CPUsExophase2016/08/23 04:08 AM
                        The (apparent) state of trace caches on modern CPUsanon2016/08/23 08:51 PM
                          The (apparent) state of trace caches on modern CPUsExophase2016/08/23 10:12 PM
                          The (apparent) state of trace caches on modern CPUsMaynard Handley2016/08/24 06:38 AM
                            The (apparent) state of trace caches on modern CPUsanon2016/08/24 07:26 PM
                    The (apparent) state of trace caches on modern CPUsMaynard Handley2016/08/23 06:48 AM
                      That's not trueDavid Kanter2016/08/23 08:39 AM
                        That's not trueMaynard Handley2016/08/23 08:56 AM
                      The (apparent) state of trace caches on modern CPUsanon2016/08/23 08:54 PM
                  The (wrong) state of trace caches on modern CPUsEric Bron2016/08/25 01:38 AM
                    The (wrong) state of trace caches on modern CPUsMichael S2016/08/25 02:28 AM
                      The (wrong) state of trace caches on modern CPUsEric Bron2016/08/25 06:12 AM
                      The (wrong) state of trace caches on modern CPUsMaynard Handley2016/08/25 08:50 AM
                        The (wrong) state of trace caches on modern CPUsMichael S2016/08/25 09:36 AM
                          The (wrong) state of trace caches on modern CPUsExophase2016/08/25 10:32 AM
                        The (wrong) state of trace caches on modern CPUsEric Bron2016/08/25 10:12 AM
                          The (wrong) state of trace caches on modern CPUsMaynard Handley2016/08/25 11:01 AM
                            The (wrong) state of trace caches on modern CPUsEric Bron2016/08/25 11:20 AM
                              The (wrong) state of trace caches on modern CPUsMaynard Handley2016/08/25 12:34 PM
        Branch/jump target predictionGabriele Svelto2016/08/11 12:15 PM
  Branch/jump target predictionGabriele Svelto2016/08/20 06:21 AM
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