[Tom's Hardware] CPU bottlenecking/frame latency benchmarks

Discussion in 'CPUs and Overclocking' started by Termie, Feb 12, 2013.

  1. BrightCandle

    BrightCandle Diamond Member

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    This again? its a well known fact the eye can perceive at least 1000 fps in some circumstances.

    And yes running 120Hz on a 60hz monitor does reduce input latency. The explanation is actually really simple.

    time =0ms
    monitor starts drawing frame0.

    time =8ms
    frame1 is done, buffer swapped.

    This will be when the monitor is half way down the transfer so the image now being sent to the monitor will have a top half of frame0 and a bottom half of frame1.

    time = 16ms
    frame2 is done, buffer swapped.

    frame0/frame1 half and half picture displayed by monitor (with some latency but its not relevant here).

    monitor starts getting frame2.

    time = 24ms
    frame 3 is done and buffer swapped.

    monitor starts getting frame3 half way down the image.

    time = 32ms
    frame 4 is done and buffer swapped.

    frame2/frame3 half and half picture displayed by monitor.

    So we can see that a perfect 120Hz will produce frames that are half 16ms old and half 8ms old. With the 8ms being the bottom half of the screen.

    In the case of vsync however the frame is all 16ms old, because that is how long it took to make it. Worse than that is it takes 16ms to send it to the monitor while the other frame is being drawn. So its actually 32ms old in all without any other buffering involved. Whereas an 8ms frame is 8ms old (render) because you only transfer it for half of the screen and we didn't have to wait for sync to get the image onto the screen. Which makes basically vsync twice the latency. Now in practice the tearing line goes all over the place and sometimes there are more than 2 frames on the screen at once. The key point to know is that the bottom of the screen is newer and that is very important for the feeling of immediate input as there is more there than in the sky normally.

    The other problem is that if the frames are unaligned. If you just so happen to have just missed a vsync then your frame is going to sit for 16ms before it even gets swapped, and then take 16ms to get to the screen, and it already took 16ms to render. So in the worst case vsync can actually cost 48ms before you start taking into account the other buffers and sources of latency. From VR headsets we know anything greater than 30ms is a real problem, it makes people sick.

    So yes 120fps on 60hz does reduce latency, and vsync off is definitely less latency than vsync on.
     
  2. boxleitnerb

    boxleitnerb Platinum Member

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    Thank you for setting that straight. Now I don't have to - you did it much better than I could anyway :)
     
  3. Arzachel

    Arzachel Senior member

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    Oh, well that's the thing I was missing. You use input latency as a measure of how long it takes for your actions to influence what you're seeing on your monitor, instead of how long it takes for your inputs to be grabbed/processed. Whoops.
     
  4. Abwx

    Abwx Diamond Member

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    That is actualy complete non sense , i hope you dont believe
    in such extraordinary claims.

    Well known by whom.??..And what are the circumstances ?.

    Theses ones ?

    Still only 100FPS , using two "frames" with a single color
    for each one , is that the way games are displayed?..

    http://en.wikipedia.org/wiki/Frame_rate
     
  5. SoulWager

    SoulWager Member

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    our eyes are much faster at detecting movement than they are at detecting changes in color(rods are faster than cones). So you need to be much more specific about what you're trying to measure.

    As for tomshardware. I'm mostly interested in the sc2 test, and their test methodology is absolute garbage. they'd be far better off downloading a macro game pro replay and benchmarking the last 5-10 minutes of it.
     
  6. nleksan

    nleksan Junior Member

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    There is a reason I joined these forums....and it's because AnandTech is one of the few TRULY LEGIT review sites out there. I used to read Tom's Hardware for reviews, but now I only read their stuff when I'm bored, and I make sure to keep my salt-shaker with me! Also, having belonged to many, many online forums (my "home" is Overclock.net), I can say without a doubt that Tom's Hardware Forums is without-contest the worst forum on a "major computer hardware site" that I've ever had the displeasure of joining.

    If you want to read REAL reviews with frame-latency being the primary means of measurement, I highly suggest heading over to TechReport. Hopefully, AnandTech will start using this methodology in their testing, because it is the ONLY thing that I think this site's reviews lack. Even without the frame latency testing, AnandTech still has the absolute best reviews on the internet, written by people who CLEARLY know what they are talking about (and who are clearly extremely well-educated), yet are also excellent writers and know how to explain some of the most complicated concepts in a way that people very new to the Enthusiast Computer World can grasp.


    I predict that it won't be long before Tom's is completely irrelevant...
     
  7. Abwx

    Abwx Diamond Member

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    Now it s no more about Fps but about movement...:rolleyes:

    Talk about changing the subject.

    You should had spared your first post for a better use
    rather than trying to spin the thing to just dismiss the said
    THG bench , according to your own words.
     
  8. blastingcap

    blastingcap Diamond Member

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    1/250th second sure, but 1000 fps (1/1000th second)??? Those are extreme situations like an air force pilot staring at a lit wall and having the silhouette of a plane flashed in front of them at 1/250th of a second, and asked to identify the plane. There might even be an afterimage. That is a far cry from, say, Far Cry on a monitor where stuff is backlit and there is the appearance of motion from one frame to another.

    I think one thing we can all agree on is that you reach diminishing returns. This like with almost anything else in life. That first 7970 is a doozy, adding a second may help, adding a third or fourth, even if they had perfect scaling, the additional fps you get going from, say, 90fps to 120fps, isn't as important as that first 30fps.
     
    #83 blastingcap, Feb 13, 2013
    Last edited: Feb 13, 2013
  9. Hubb1e

    Hubb1e Senior member

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    Everyone keeps arguing over the test methodology, but regardless of the methodology, there is a clear trend, and that is AMD's MOAR CORES strategy is helping them in the long run overcome some of their per core performance issues.

    Tomshardware has for over a year recommended Intel 2 core Pentium chips for budget gamers, and I have continued to argue that they were being short sighted. Some of the comparable AMD chips were just barely behind the Pentium and still provided playable framerates, but had more cores that were not well used in their benchmarks. As new games came out they were increasingly threaded, so those extra cores were being used while the Pentium fell behind. AMD and Intel could deliver playable framerates in current games, and future games were increasingly threaded, making the AMD chips a better fit for longevity and that was shown in this review. They have had to change their recommendations for budget chips from the Pentiums to the Phenom IIs.

    Now, you could always drop in an i5 into a 1155 motherboard, so the Pentium recommendation wasn't a terrible one, but the AMD chips deserved more than they were getting from Toms. And, as the consoles launch with 8 threads the 6 and 8 core AMD chips may also see additional performance increases.

    Down in the sub $200 CPU marketplace, I think AMD is at least competitive and when you take overclocking into account, the AMD chips look pretty good. But, as you approach $200 it really makes no sense to buy anything but an i5k. Down below $150 AMD still has some good chips.
     
  10. boxleitnerb

    boxleitnerb Platinum Member

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    In certain engines more fps make the controls much more direct. Why do you think pro gamers like playing with high fps? I know some BF3 gamers who state that their scores are better at higher fps. Personally I can absolutely distinguish between 30 and 60fps and sometimes between 60 and 120fps, depending on the engine.

    I think BrightCandle explained it quite well. It's about how old the displayed image is, about the current game state. 16ms between displayed frames (60Hz) is a long time. If all goes wrong, the displayed image and game state are almost 16ms apart. But if you have twice the fps, the displayed image would represent the current game state much more accurately, because there are more frames for vsync "to select from". Sorry if my explanation is crude, but that is how I would see it.
     
  11. dqniel

    dqniel Senior member

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    Thank you.

    I feel like I'm taking crazy pills when people claim that with a 60Hz LCD you can't tell a difference once you're beyond 60FPS. The same goes with going past 120FPS on a 120Hz LCD. There IS a difference.

    Anybody who's played a competitive FPS on the Q3 engine knows that even when playing on a 60Hz LCD there is a noticeable difference in smoothness and input lag when going from 60 fps to 125 fps to 250 fps to even 333 fps... and I'm not talking about the engine glitches resulting in higher jumping. Go to a competitive FPSer's house and do a double blind test with them, they'll be able to tell the difference between 125, 250, and 333fps with VSYNC disabled in any Q3 engine game supporting those framerates... every single time. It's also easily distinguishable in the UE3-based games.
     
    #86 dqniel, Feb 13, 2013
    Last edited: Feb 13, 2013
  12. Zink

    Zink Senior member

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    I think their new testing is also very useless for comparing CPUs. They are using the "difference between the time it takes to display consecutive frames". This means that a slow CPU that is bottlenecking and always takes 150ms to render every frame will score better than a fast CPU that gets GPU bound and so varies between 50ms and 100ms a frame. It is still a much better experience than the low end CPU. Why don't they just stick to measuring the 99th percentile frame times like other sites do?
    It is strange that they made up this complex system that doesn't show my anything useful. Maybe I just don't understand? The only way this seems like it would be useful is comparing two CPUs with identical fps like they do at the start of the article.
     
  13. Zink

    Zink Senior member

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    Case in point: The two Far Cry 3 graphs from the OP.
    The two lowest performance CPUs are way at the top of the "latency" chart. How is this a useful ranking??? They are consistently bad?
     
  14. Concillian

    Concillian Diamond Member

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    This was my original point. The way Tom's is reporting this, their data is not very relevant to or translatable to real world performance. The chosen percentiles are arbitrary, and in most cases even the 95th percentile latencies of the worst CPUs reviewed are likely low enough to be considered "perfect" to human eyes.
     
  15. ThePeasant

    ThePeasant Member

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    One thing has become clear to me; they really need to thoroughly explain how and what it is they are measuring. Whatever statistical method they are using is unfamiliar to me.
     
  16. Idontcare

    Idontcare Elite Member

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    I suspect they are grappling with it, stumbling through the dark towards a light in the far off distance, the same as the TechReport and the rest of us.

    Everyone knows something is there, no one has managed to fully flesh it out yet is all.

    Reminds me so much of the early days of SSDs with the anecdotal and unqualified reports of stuttering and hanging on drives. Lots of people spoke to the problem, a few tried to characterize and qualify the observations, but it wasn't until Anand spent weeks and weeks cracking that nut before we could all realize what it was that was wrong with SSDs up until then.

    Something tells me this issue with GPUs is going to come out in similar fashion. We are all (including various reviewers) going to be stumbling around in the dark on this one, looking at the shadows cast on a wall, knowing something is amiss but having the reality of it remain just ever so far away that we can't grasp it firmly...but then one day someone will crack it and everybody and their brother is going to slap their foreheads and yell "of course! it is so simple!".

     
  17. Forde

    Forde Member

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    Can someone please explain this to me in simple terms? What is the difference between Tom's and Tech Report's review on this matter? As a gamer, which graphs should I be looking at?

    I have an FX-4170 and I'm trying to understand how it compares to the i3-3220 / 2100 in gaming. Tom's shows it faring better, Tech Report says the other way around... so which one is it?