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Thread: Latency on linux

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  1. #1

    Default Latency on linux

    Hello,

    I'm not sure to be into the right forum.
    To follow this french article:
    http://www.pcworld.fr/carte-graphiqu...e,534679,1.htm
    The max latency is very important. I have noted under linux: correct FPS but some time a big latency/FPS slow down. Same for my hdd.
    Phoronix should include in their test the latency check for graphic card (I have have big slow down when I'm playing and kopete/skype open a window). And for hdd when you you have file copy in progress in graphic (KDE/Gnome?) and you try open an application (like chrome, with multiple small file to open).
    I have sometime latency when I write into kwrite... about 500~3000ms after I have press the key is displayed on my screen.

    Cheer,
    Last edited by alpha_one_x86; 01-04-2013 at 04:30 AM.

  2. #2
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    Quote Originally Posted by alpha_one_x86 View Post
    (I have have big slow down when I'm playing and kopete/skype open a window).
    This is probably compositing: If you have a fullscreen game the window manager probably "unredirects" it so the game is directly rendered on the screen. When there is another window visible, even a notification, then everything on the desktop will be "redirected" to the compositor.
    Compositing should have very little impact but in practice it seems that it doesn't work so well and there are big slowdowns.

    Quote Originally Posted by alpha_one_x86 View Post
    And for hdd when you you have file copy in progress in graphic (KDE/Gnome?) and you try open an application (like chrome, with multiple small file to open).
    There seems to still be a problem in determining how to autotune disk access for the best interactivity. I think it got pretty good on linux in the last one or two years. There are still situations where you get huge slowdowns because of disk access but I don't think any operating system has solved this completely yet. I have observed similar things in windows 7. But just sometimes.

    Quote Originally Posted by alpha_one_x86 View Post
    I have sometime latency when I write into kwrite... about 500~3000ms after I have press the key is displayed on my screen.
    Three seconds? You mean, even if the computer/hard disk is otherwise idle? Is it in other text editors too? If not, then it may be the fault of a kate plugin.



    And related to the FPS. Just yesterday I have tried a bit skyrim in windows 7 on a middle class notebook with the newest stable catalyst from amd.com. It definitely has problems with latency. Sometimes even if fraps displays 40+ FPS I see a very noticeable micro stutter. So it probably depends on multiple factors like the game, the drivers, the scheduler, etc.
    Last edited by ChrisXY; 01-04-2013 at 10:18 AM.

  3. #3

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    Quote Originally Posted by ChrisXY View Post
    Three seconds? You mean, even if the computer/hard disk is otherwise idle? Is it in other text editors too? If not, then it may be the fault of a kate plugin
    Mostly my problem is when I play video, more I have X work (new windows, effect, widget redraw, ...). My worst case I video HD + game in windowsed mode, in this case windows 7 work, linux have big slow down.
    I have middle graphic card, quad core cpu, 8GB of memory, ssd for the OS. Then correct computer. All is fast in console only. More difficult: Dual screen, multiple virtual desktop.

    Quote Originally Posted by ChrisXY View Post
    Sometimes even if fraps displays 40+ FPS I see a very noticeable micro stutter. So it probably depends on multiple factors like the game, the drivers, the scheduler, etc.
    In the case of 7000+ serie, the amd drivers have a problem.

    I things a benchmark of all linux factor will help the dev to see and solve the problem (drivers, scheduler, X/Wayland?, ...). But no on FPS, on max latency.

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    Quote Originally Posted by alpha_one_x86 View Post
    My worst case I video HD + game in windowsed mode, in this case windows 7 work, linux have big slow down.
    I think I know this effect.

    When running furmark in wine I also get massive slowdowns in X. http://www.ozone3d.net/benchmarks/fur/

    But it usually doesn't happen for normal games, only at extreme gpu stress.

  5. #5
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    Phoronix should include in their test the latency check for graphic card
    While I agree it's a good idea, that doesn't exist, ergo somebody needs to write it. So far nobody's done so, though I recall someone started on making Doom 3 report that after a timedemo.

    Do we have a volunteer?

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    Quote Originally Posted by alpha_one_x86 View Post
    Mostly my problem is when I play video, more I have X work (new windows, effect, widget redraw, ...). My worst case I video HD + game in windowsed mode, in this case windows 7 work, linux have big slow down.
    I have middle graphic card, quad core cpu, 8GB of memory, ssd for the OS. Then correct computer. All is fast in console only. More difficult: Dual screen, multiple virtual desktop.


    In the case of 7000+ serie, the amd drivers have a problem.

    I things a benchmark of all linux factor will help the dev to see and solve the problem (drivers, scheduler, X/Wayland?, ...). But no on FPS, on max latency.
    Playing a game while watching a movie is something that I have always had difficulties with. I ended up buying a second video card to plug the second monitor into and now its smooth as warm butter.

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    They've been doing some interesting stuff over at pcper lately
    http://www.pcper.com/reviews/Graphic...ormance-Metric
    I'd think that should work well with linux too since it's a dedicated external system capturing the output
    I notice stuttering in unigine tropics benchmark personally, I wonder if that's fglrx or just the benchmark itself.

  8. #8
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    Actually, this wouldn't even be a huge job, maybe 8 hours or so. Anyone wanna hire me?

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