8 Replies Latest reply on May 19, 2018 12:56 AM by wimpzilla

    Crossfire, Lowest Common Denominator?


      It had been years since I built a gaming machine and over the past three months I have cobbled a new one together as i forgot how much i enjoyed the building process.  My build is as follows:


      i7 8700K

      Asus ROG STRIX Z370-E

      16 GB Corsair Vengence RGB DDR4

      2 x Corsair Force LS SSD

      2 x Corsair Force GT SSD

      2 x Lite On SSD

      Corsaive HX850i

      Thermaltake Core P5

      EKWB Custom Loop Cooling

      XFX RX 580 8GB (Primary) (Purchased when RMA took three months)

      XFX RX 570 4GB (Linked) (From RMA'd RX 560)


      I have a couple of questions.  One, is that I was under the impression that when running in crossfire mode all cards follow the lowest common denominator, so in my case they should both act like the RX 570 correct?  That did not seem to be the case at all.  I did some testing in Far Cry 5 and while it absolutely shows that it was running in Crossfire, it was doing so at the RX 580 speed and using all 8GB of VRAM.  Did I do something wrong?


      My second question is that when I go into Radeon settings I see that the core clock and memory speed of the RX 570 are wonky, it says 1100 core clock and 1850 memory speed when it should say 1286 core clock and 1750 memory speed.  What could cause this, is it a function of the Crossfire feature?


      I am thrilled with the results but want to make sure I am not doing something wrong.


      Far Cry 5 (3440x1440, Ultra, RX 580 Only)

      Minimum FPS = 36

      Maximum FPS = 52

      Average FPS = 41


      Far Cry 5 (3440x1440, Ultra, RX 580 + RX 570 CF)

      Minimum FPS = 43 (+19%)

      Maximum FPS = 79 (+52%)

      Average FPS = 63 (+50%)


      As I said the gains were awesome to see from the entire situation.

        • Re: Crossfire, Lowest Common Denominator?



          So to answer your questions:


          Remember that the crossfire behave differently depending the game, engine used.
          Also it mean that the crossfire will not behave the same, using different versions of direct X.
          So the crossfire scaling depend from a lot of factors, game, engine, directX, hardware, etc.
          If you take FC5 as example, it run an engine under DX12 with enhanced features for crossfire and multi-gpu in general.
          So on optimized games, the engine, DX/Os recognize both card separately loading them both equally with great results!
          On the other hand, if the environment is not well optimized, the scaling is lower, the cards are not evenly used and ran on the slowest one.
          That's why the crossfire is a great feature but not always easy to max the fps scaling, maybe it will evolve into multi-gpu for wide ranges purposes in future.


          What really count and matter is your clocks under load. Download GPU-z it display T°, voltages monitoring.
          Also you could DDU to clean the driver and reinstall the latest ones, maybe the card do not boost to it's max clocks when in crossfire.
          I would advice you to have aslo some fun benching 3Dmark, Heaven, Superposition checking your crossfire behaviour.
          If you feel something unusual, you can also report it using the AMD Report Form, easy to google it.

          1 of 1 people found this helpful
            • Re: Crossfire, Lowest Common Denominator?



              Thanks for the response.  I figured given the amount of time that Far Cry 5 has spent being advertised in the Radeon settings it was set up to be optimized for Crossfire.  I looked it up the two games I primarily play Far Cry 5 and Project Cars 2 which both have decent Crossfire profiles.


              I am starting fresh with a fresh installation of Windows 10 64-bit and everything else.  I will do as you suggested and play with the benchmarks and see what happens with and without crossfire enabled.


              Thanks again.

                • Re: Crossfire, Lowest Common Denominator?

                  That was actually a lot of fun running the benchmarks last night.  I turned on the Crossfire logo so I could ensure when it was actually being used in the benchmarks.  Interestingly enough the 3DMark one, the logo did not appear on with Crossfire enabled so I am assuming that it was not on.  If it was then there was a negligible difference between the two.


                  As for Heaven and Valley the difference was amazing.  I was getting on average +70% performance gains from Crossfire!  I am not sure how to do a screen capture of the video but it was very evident.


                  Heaven and Valley limited themselves to 4GB of memory so that was following the lowest common denominator however in Project Cars 2 and Far Cry 5 the GPU-Z Log showed topping out in the 7GB range, so that is awesome.


                  Also the clean install was the key to everything.  The 570 is now clocking @ 1386 Mhz on the core and 1750 Mhz on the memory in the Radeon settings information.  Something unexpected did happen however during both benchmarks and game play in Far Cry 5 and Project Cars 2.  The logs show the RX 570 running at 1425 Mhz on the core and 2025 Mhz on the memory.  This is the OC+ numbers that are in Wattman for the RX 580.  The 3Dmark system information also showed something similar and instead of two different cards showed 2 x RX 580.


                  Is the diffeence between the 570 and the 580 only speed or is there something else that I am missing?

                    • Re: Crossfire, Lowest Common Denominator?



                      I'm happy you took some good time benching, it's always fun check how the hardware behave in different scenarios.
                      To answer to your question, the only difference between the RX580 and the RX570 is the number of CU within the gpu.
                      The RX580 care 2304 Steam Processors so 36CU, the RX570 2048SP so 32CU, but the chip itself is the same.
                      Then the RX570 care maybe some other kind of memory chip and have a lower TDP, power consumption.


                      About the clocks, it's quite unexpected for the RX570 to boost so high, especially because the best silicon would go toward the RX580 cards.
                      That's also why the RX580 have higher boost clocks than the RX570, this not mean that the RX570 can't achieve these clocks.
                      It would maybe required more voltage to do so and suit better to a RX570 card class.
                      So not sure the software read correctly both card, maybe it mistake with the RX580? What GPU-z said about, you have a tab for each card on the bottom?


                      Last thing, dunno if you can but try also other games in DX11/DX12 and superposition benchmark, an updated version of heaven/valley.
                      Also not sure why you would not have any scaling in 3Dmark, it should scale quite nicely.

                        • Re: Crossfire, Lowest Common Denominator?



                          I decided to start over again at the suggestion of XFX, the card manufacturer, with the installation of everything.  What they wanted was me to install one card at a time and then restart each time.  After doing so I ran benchmarks again and am getting similar results.  The only change is that the audio driver for the 570 is now having issues.  I cannot believe it is doing so well in general though.


                          In general I am seeing a 50-70% increase in performance using Crossfire.  All the games I play seem to scale well.  What I do find interesting is that the system needs to start using crossfire takes about 2 seconds at the beginning of games or benchmarks.


                          Thank you for all your help wimpzilla.  I really do appreciate it.

                            • Re: Crossfire, Lowest Common Denominator?



                              Well XFX guy was peaking sense it seems, what he advices you to do is the general good practice to troubleshoot crossfire issues.
                              Usually you plug a card 1st, then thge second at reboot, usually it help solving crossfire detection issue.
                              But this procedure is meant to solve issues, not boosting the performances.


                              So i would say your crossfire is working fine, 50/70% of gain is what usually one get, depending drivers and games.
                              If you got and issue with the HDMI audio, just DDU the drivers with the safe mode option, then reinstall the latest ones with both card plugged, see if it change something.
                              I'm not aware of any delays, my last crossfire was HD4870/HD4890, but i can inquire about and let you know!

                              Remember that the crossfire is really games and driver dependant, so when you have time and want to have fun, compare old vs new drivers, there is always something to discover about, i suppose. ^^


                              You are welcome!

                      • Re: Crossfire, Lowest Common Denominator?

                        Isn't FC5 a DX11 game?