Thanks Andreas. On Tue, Oct 23, 2012 at 4:36 PM, Andreas Hansson <andreas.hans...@arm.com>wrote:
> Mitch is spot on I think. > > The latencies are for that specific block, caches, busses, memory > controllers etc. > > Andreas > > From: mihai pricopi <mihai.pric...@gmail.com<mailto: > mihai.pric...@gmail.com>> > Reply-To: gem5 users mailing list <gem5-users@gem5.org<mailto: > gem5-users@gem5.org>> > Date: Tuesday, 23 October 2012 09:35 > To: gem5 users mailing list <gem5-users@gem5.org<mailto: > gem5-users@gem5.org>> > Subject: Re: [gem5-users] Perfect branch predictor in ooo > > Thanks :) indeed I think is the only way possible. > > Can I ask one more question regarding L2 and memory latency ? > > For a L2 cache access the latency is computed by (L1.latency + L2.latency) > or is the L2.latency ? > Similarly for memory ? > > On Tue, Oct 23, 2012 at 10:54 AM, Mitch Hayenga < > mitch.hayenga+g...@gmail.com<mailto:mitch.hayenga+g...@gmail.com>> wrote: > No, that would not be enough. Doing that change would just make the front > end assume no branch was ever taken (and the sim would actually crash > because the commit logic would later would try to inform the front end > about branches it never predicted). > > To do this (with the saving branch outcomes to a file & later just > replaying them as if you had predicted them right the first time), you'd > have to hook the proper spaces in the squash/update functions in > bpred_unit_impl.hh to figure out what the correct predictions should have > been. Then save these correct decisions off to a gzipped file (I haven't > thought how big this is going to be, but this file will be pretty massive). > Then re-run the simulation with the "predict" from bpred_unit_impl.hh just > feeding the correct path information from this file. > > > On Mon, Oct 22, 2012 at 9:14 PM, mihai pricopi <mihai.pric...@gmail.com > <mailto:mihai.pric...@gmail.com>> wrote: > Thanks. > Would be enough to change a bit the lookupAndUpdateNextPC() function such > that the return is always false ? > I mean changing the: > > if (!inst->isControl()) { > TheISA::advancePC(nextPC, inst->staticInst); > inst->setPredTarg(nextPC); > inst->setPredTaken(false); > return false; > } > > > to > > // if (!inst->isControl()) { > TheISA::advancePC(nextPC, inst->staticInst); > inst->setPredTarg(nextPC); > inst->setPredTaken(false); > return false; > // } > > ? > > > On Tue, Oct 23, 2012 at 10:02 AM, Mitch Hayenga < > mitch.hayenga+g...@gmail.com<mailto:mitch.hayenga+g...@gmail.com>> wrote: > Since gem5 the O3 cpu model actually executes instructions @ execute (not > fetch/decode) a perfect branch predictor is a bit tricky. Assuming you are > running a single-threaded app in SE mode (so you don't have > OS/multi-threaded time variance issues), you could simply run the > application twice. Save the branch outcomes from the first run. Then > re-run the app, with a "predictor" that just uses the branch results from > the first time you ran the application. > > On Mon, Oct 22, 2012 at 8:43 PM, mihai pricopi <mihai.pric...@gmail.com > <mailto:mihai.pric...@gmail.com>> wrote: > Hi, > > I am using arm_detailed SE mode. > Is there a simple way to force the branch predictor to do perfect > prediction ? > > Thanks > > _______________________________________________ > gem5-users mailing list > gem5-users@gem5.org<mailto:gem5-users@gem5.org> > http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users > > > _______________________________________________ > gem5-users mailing list > gem5-users@gem5.org<mailto:gem5-users@gem5.org> > http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users > > > _______________________________________________ > gem5-users mailing list > gem5-users@gem5.org<mailto:gem5-users@gem5.org> > http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users > > > _______________________________________________ > gem5-users mailing list > gem5-users@gem5.org<mailto:gem5-users@gem5.org> > http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users > > > -- IMPORTANT NOTICE: The contents of this email and any attachments are > confidential and may also be privileged. If you are not the intended > recipient, please notify the sender immediately and do not disclose the > contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you. > > _______________________________________________ > gem5-users mailing list > gem5-users@gem5.org > http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users >
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