Update to Intel Optimization Manual

By: anon (anon.delete@this.anon.com), October 1, 2015 10:45 pm
Room: Moderated Discussions
Patrick Chase (patrickjchase.delete@this.gmail.com) on October 1, 2015 5:16 pm wrote:
> David Kanter (dkanter.delete@this.realworldtech.com) on October 1, 2015 1:52 pm wrote:
> > Patrick Chase (patrickjchase.delete@this.gmail.com) on September 30, 2015 10:44 pm wrote:
> > > SHK (no.delete@this.mail.com) on September 29, 2015 6:38 am wrote:
> > > > * page split load penalities from 100 cycles to 5 (that's an improvement!)
> > >
> > > This appears to be a side-effect of having a second HW page-table walker - In a page-
> > > split-load scenario the core should now handle both walks in // instead of sequentially.
> > >
> > > The true benefits are much broader than that (relatively uncommon) case, though.
> >
> > I read this as: a page crossing load which hits in the TLB for both pages now takes
> > 5 cycles instead of 100. That is, I don't think the page table walker is involved.
> >
> > Obviously, if you have a TLB miss - nothing will take anywhere close to 5 cycles.
>
> I read that section as saying that the incremental cost (i.e. the penalty) for a page-split
> load above and beyond the cost of one that doesn't split was reduced from 100 cycles to 5,
> in which case the difference (95 cycles) is credible for 2 walks in // vs 2 sequentially.

Considering that split cacheline load is 5 cycles (on Haswell), I don't think it's credible that they could do a split load, miss TLB, then kick off the second tlb miss handler, complete them, then redo the split load from L1 (assuming you have an L1 hit) all in the same number of cycles as a split cacheline. Seems more likely they just added some improved mechanism to atomically look up 2 TLB entries without some big exception, so the load can proceed from there as any other split cacheline load.

< Previous Post in Thread 
TopicPosted ByDate
Update to Intel Optimization ManualSHK2015/09/29 05:38 AM
  gather speedEric Bron2015/09/29 09:43 AM
    gather speedGabriele Svelto2015/09/29 12:00 PM
  Update to Intel Optimization ManualTim McCaffrey2015/09/29 11:18 AM
    Update to Intel Optimization ManualSHK2015/09/29 12:04 PM
      Update to Intel Optimization ManualAnon2015/09/29 02:23 PM
    Update to Intel Optimization Manualnone2015/09/29 10:31 PM
      Update to Intel Optimization ManualMichael S2015/09/30 04:24 AM
    Update to Intel Optimization ManualMichael S2015/09/30 04:30 AM
      Update to Intel Optimization ManualTim McCaffrey2015/09/30 10:01 AM
  5-6 wide core, why no mention from Intel?Wouter Tinus2015/09/30 02:14 PM
    5-6 wide core, why no mention from Intel?Maynard Handley2015/09/30 03:30 PM
      5-6 wide core, why no mention from Intel?Alberto2015/10/01 12:13 AM
        5-6 wide core, why no mention from Intel?anon2015/10/01 02:21 AM
          5-6 wide core, why no mention from Intel?Alberto2015/10/01 04:41 AM
            5-6 wide core, why no mention from Intel?anon2015/10/01 05:27 AM
              5-6 wide core, why no mention from Intel?Alberto2015/10/01 08:33 AM
                5-6 wide core, why no mention from Intel?juanrga2015/10/01 10:24 AM
        5-6 wide core, why no mention from Intel?Maynard Handley2015/10/01 08:57 AM
    5-6 wide core, why no mention from Intel?juanrga2015/10/01 03:59 AM
      5-6 wide core, why no mention from Intel?Wouter Tinus2015/10/01 02:48 PM
        5-6 wide core, why no mention from Intel?juanrga2015/10/03 03:17 AM
          5-6 wide core, why no mention from Intel?Wouter Tinus2015/10/03 11:19 AM
            Are you kidding? (NT)juanrga2015/10/04 05:30 AM
              Are you kidding?Wouter Tinus2015/10/04 03:18 PM
                Are you kidding?juanrga2015/10/05 09:46 AM
                  Are you kidding?David Kanter2015/10/05 11:24 AM
                    Are you kidding?anon2015/10/05 09:26 PM
                    Are you kidding?Linus Torvalds2015/10/07 04:49 AM
                      Are you kidding?juanrga2015/10/07 10:46 AM
                        Are you kidding?anon2015/10/07 06:21 PM
                  Are you kidding?Wouter Tinus2015/10/05 01:25 PM
                    Are you kidding?juanrga2015/10/06 10:17 AM
                      Are you kidding?Stubabe2015/10/07 12:17 AM
                        Are you kidding?juanrga2015/10/07 10:56 AM
                          Amazing...Wouter Tinus2015/10/07 11:31 AM
                            Amazing...juanrga2015/10/07 03:45 PM
                          Are you kidding?Stubabe2015/10/07 11:57 AM
                            Are you kidding?juanrga2015/10/07 03:59 PM
                          Are you kidding?Wilco2015/10/07 02:07 PM
                            Are you kidding?juanrga2015/10/07 04:33 PM
      5-6 wide core, why no mention from Intel?Eric Bron2015/10/04 04:18 AM
    5-6 wide core, why no mention from Intel?David Kanter2015/10/01 09:01 AM
      Optimal number and kind of execution unitsjuanrga2015/10/01 10:50 AM
        Optimal number and kind of execution unitsPatrick Chase2015/10/01 04:38 PM
          Optimal number and kind of execution unitsI.S.T.2015/10/01 05:10 PM
            Optimal number and kind of execution unitsPatrick Chase2015/10/01 11:39 PM
          Optimal number and kind of execution unitsExophase2015/10/01 10:11 PM
          Optimal number and kind of execution unitsjuanrga2015/10/02 05:14 AM
      LD/ST unitsSHK2015/10/01 11:11 AM
        LD/ST unitsDavid Kanter2015/10/01 12:54 PM
          LD/ST unitsSHK2015/10/02 04:55 AM
            LD/ST unitsJukka Larja2015/10/02 09:49 PM
        LD/ST unitsMaynard Handley2015/10/01 01:01 PM
          LD/ST unitsanon2015/10/01 09:54 PM
      5-6 wide core, why no mention from Intel?Maynard Handley2015/10/01 12:57 PM
        5-6 wide core, why no mention from Intel?David Kanter2015/10/01 03:49 PM
          5-6 wide core, why no mention from Intel?Maynard Handley2015/10/01 06:21 PM
          5-6 wide core, why no mention from Intel?Exophase2015/10/01 10:07 PM
            5-6 wide core, why no mention from Intel?Maynard Handley2015/10/02 12:10 AM
              5-6 wide core, why no mention from Intel?Megol2015/10/02 03:39 AM
                5-6 wide core, why no mention from Intel?Michael S2015/10/02 04:27 AM
                5-6 wide core, why no mention from Intel?Maynard Handley2015/10/02 09:37 AM
                  5-6 wide core, why no mention from Intel?noko2015/10/02 05:19 PM
              5-6 wide core, why no mention from Intel?Exophase2015/10/02 06:43 AM
                5-6 wide core, why no mention from Intel?Maynard Handley2015/10/02 09:45 AM
                  5-6 wide core, why no mention from Intel?Exophase2015/10/02 10:23 AM
          5-6 wide core, why no mention from Intel?Wilco2015/10/02 12:48 PM
            5-6 wide core, why no mention from Intel?Maynard Handley2015/10/02 01:25 PM
              5-6 wide core, why no mention from Intel?Wilco2015/10/02 02:26 PM
              5-6 wide core, why no mention from Intel?noko2015/10/02 05:45 PM
                5-6 wide core, why no mention from Intel?Maynard Handley2015/10/02 06:54 PM
            5-6 wide core, why no mention from Intel?David Kanter2015/10/02 01:59 PM
              5-6 wide core, why no mention from Intel?Wilco2015/10/02 02:59 PM
                5-6 wide core, why no mention from Intel?David Kanter2015/10/02 03:15 PM
                  5-6 wide core, why no mention from Intel?Wilco2015/10/02 04:06 PM
                    LDP/STP usage in AArch64 for 403.gccnone2015/10/03 01:04 AM
                      LDP/STP usage in AArch64 for 403.gccWilco2015/10/03 03:02 AM
                        LDP/STP usage in AArch64 for 403.gccnone2015/10/03 03:11 AM
                          LDP/STP usage in AArch64 for 403.gccWilco2015/10/03 03:37 AM
                            LDP/STP usage in AArch64 for 403.gccnone2015/10/03 04:37 AM
                              LDP/STP usage in AArch64 for 403.gccWilco2015/10/03 05:26 AM
                  5-6 wide core, why no mention from Intel?Maynard Handley2015/10/02 04:24 PM
              5-6 wide core, why no mention from Intel?Maynard Handley2015/10/02 03:07 PM
  Update to Intel Optimization Manualanon2015/09/30 04:43 PM
  Update to Intel Optimization ManualPatrick Chase2015/09/30 09:44 PM
    Update to Intel Optimization Manualanon2015/09/30 10:49 PM
    Update to Intel Optimization Manualnone2015/09/30 10:50 PM
    Update to Intel Optimization ManualDavid Kanter2015/10/01 12:52 PM
      Update to Intel Optimization ManualPatrick Chase2015/10/01 04:16 PM
        Update to Intel Optimization Manualanon2015/10/01 10:45 PM
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