Sign in to follow this  
Prune

OpenGL Video RAM fragmentation and resource management for continuously running system?

Recommended Posts

Basically I don't know how to handle this situation: Consider a continuously running system which loads and unloads modules based on a schedule very frequently (on average every minute) but the OpenGL rendering never leaves full-screen; the module switch is completely seamless (maybe a half-second fade in between one module stopping drawing to the OpenGL render thread and the next starting). Now, since I can't preload all the data simultaneously at system startup , and things like textures and VBOs will have to be dynamically loaded, how do I avoid video memory fragmentation from eventually killing performance (and possibly stability)? I need the system to be very stable and cannot do restarts more often than once in 24 hours (preferably once a week).

Share this post


Link to post
Share on other sites
First load in all the data that won't be changing between module loads/unloads, if any. After that, load in a module's texture data. When the module is done, unload it completely before loading the next module data. If you do it this way, there won't be any fragmentation.

Share this post


Link to post
Share on other sites
Quote:
Original post by Promit
Is this actually an observed problem, or just paranoia?

My boss wants a system that is near unconditionally stable. I better be paranoid if I want to keep my job.

Quote:
Original post by Numsgil
First load in all the data that won't be changing between module loads/unloads, if any. After that, load in a module's texture data. When the module is done, unload it completely before loading the next module data. If you do it this way, there won't be any fragmentation.

Thanks for the suggestion. I'm wondering what the best way is to load stuff so that I can do a quick switchover. I would have to preload stuff for the next module before the first is finished, but I'm wondering if a whole bunch of glTexImage, glBufferData, and glMapBuffer will not screw up framerate of whatever's currently running. I could have the next module queueing messages to the render thread to do these with some sparseness (in time) but that seems like not the simplest solution.

Share this post


Link to post
Share on other sites
In that case, you're going to have to do heavy stress testing anyway. Why not write a simpler first pass implementation, and then refine based on what you see?

Share this post


Link to post
Share on other sites
I guess just that in my experience major refinements end up being rewrites of half the stuff heh...

Numsgil's suggestion requires that I unload a module completely before loading the next one. That's a problem in terms of seamlessly going from one to the other, with a half-second black screen or logo being displayed between them acceptable. I'd really need to start loading the next one before unloading the current.

Now imagine doing such a switch around every minute for 24 hours. How likely that video memory would get fragmented and it'll end up with constant swapping with main memory?
At least with system RAM there there is a clear solution--preallocate memory pools. But no void* analogue for VRAM; to do memory management there would be a pain since there'd be preallocate 'free' lists of all different types of objects such as texture with x channels and y resolution (with glTexImage2D), and checking the list for a match to put the new texture in with glTexSubImage2D when loading actual textures, then sending back to free list (example at http://www.codeguru.com/cpp/g-m/opengl/texturemapping/article.php/c5573/ ), and then for VBOs there'd be something like this, etc. and it'll be horrible...

Share this post


Link to post
Share on other sites
The completely-unload-one-before-loading-the-next is the method we're using at work. In our experience unloading a level/module/whatever should be nearly instantaneous. Certainly not anywhere near as long as loading a level/module/whatever. This makes sense when you consider that the driver doesn't have to upload any data to the card when it unloads a texture, it just deletes a handle somewhere.

Share this post


Link to post
Share on other sites
Sure, the unloading is near instantaneous, but the loading isn't. That's the problem. Consider timeline:

<--0.5sFadeIn----1minModule1Draws-----0.5sFadeOut--><--0.5sSplash--><--0.5sFadeIn----1minModule2Draws-----0.5sFadeOut-->... [to module n then repeat]

After one module finishes running I can't go much over half a second till the second starts drawing. So completely unloading the first before loading the second doesn't seem viable.

Share this post


Link to post
Share on other sites
what you could do is to load the resource you need to load (textures, vbo, etc...) in system mem buffers only (you can do this asynchronously - in a loading thread).

Once all the resources have been loaded into RAM, unload your previous module (including GPUs objects), then simply creates you GPUs buffer and fill them from you RAM buffers. That should be pretty fast, at least this should be the fastest solution (appart from sharing resource between modules, i.e. re-using texture objects/vbo - but this is nearly impossible as they should all have the same size...)

Share this post


Link to post
Share on other sites
gjaegy, that's the approach I intend to start with. I thought about virtual texturing but the complexity and shader overhead are a turnoff...

Quote:
Original post by V-man
module?

Mostly independent media content packages, such as games, videos, etc. Since the functionality of each is different, i.e. game logic, animation, simulation, rendering and GI algorithms, etc., they're individual dynamically linked (at runtime) libraries and associated data, and only a small subset will fit in memory at a time, in general. The system is non-deterministic due to users interaction, but it needs to run without supervision and users are not intended to have any supervisory role whatsoever and can only interact with the content, not the system it runs on. That's about as descriptive as I can be without violating my NDA LOL

Share this post


Link to post
Share on other sites
Some will be small and all of those could be preloaded. But some will be using around a GB of RAM (I already have one that does that).
There will be around a dozen or so modules running one after another, and then the cycle repeats indefinitely.
I'm ignoring for now the problem of system memory fragmentation if I'm loading from HD (very likely given the memory limit on a 32-bit system), but might do a custom new/delete for that if it's a problem.

Share this post


Link to post
Share on other sites
Quote:
Original post by Prune
Some will be small and all of those could be preloaded. But some will be using around a GB of RAM (I already have one that does that).
And how much data will be shared between modules?

It sounds like you should be able to load all the new assets into RAM, and then flush out all the data in the GPU and submit the new data. This way you can preload from the HD, and you shouldn't have any fragmentation in the GPU.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Forum Statistics

    • Total Topics
      627719
    • Total Posts
      2978797
  • Similar Content

    • By DelicateTreeFrog
      Hello! As an exercise for delving into modern OpenGL, I'm creating a simple .obj renderer. I want to support things like varying degrees of specularity, geometry opacity, things like that, on a per-material basis. Different materials can also have different textures. Basic .obj necessities. I've done this in old school OpenGL, but modern OpenGL has its own thing going on, and I'd like to conform as closely to the standards as possible so as to keep the program running correctly, and I'm hoping to avoid picking up bad habits this early on.
      Reading around on the OpenGL Wiki, one tip in particular really stands out to me on this page:
      For something like a renderer for .obj files, this sort of thing seems almost ideal, but according to the wiki, it's a bad idea. Interesting to note!
      So, here's what the plan is so far as far as loading goes:
      Set up a type for materials so that materials can be created and destroyed. They will contain things like diffuse color, diffuse texture, geometry opacity, and so on, for each material in the .mtl file. Since .obj files are conveniently split up by material, I can load different groups of vertices/normals/UVs and triangles into different blocks of data for different models. When it comes to the rendering, I get a bit lost. I can either:
      Between drawing triangle groups, call glUseProgram to use a different shader for that particular geometry (so a unique shader just for the material that is shared by this triangle group). or
      Between drawing triangle groups, call glUniform a few times to adjust different parameters within the "master shader", such as specularity, diffuse color, and geometry opacity. In both cases, I still have to call glBindTexture between drawing triangle groups in order to bind the diffuse texture used by the material, so there doesn't seem to be a way around having the CPU do *something* during the rendering process instead of letting the GPU do everything all at once.
      The second option here seems less cluttered, however. There are less shaders to keep up with while one "master shader" handles it all. I don't have to duplicate any code or compile multiple shaders. Arguably, I could always have the shader program for each material be embedded in the material itself, and be auto-generated upon loading the material from the .mtl file. But this still leads to constantly calling glUseProgram, much more than is probably necessary in order to properly render the .obj. There seem to be a number of differing opinions on if it's okay to use hundreds of shaders or if it's best to just use tens of shaders.
      So, ultimately, what is the "right" way to do this? Does using a "master shader" (or a few variants of one) bog down the system compared to using hundreds of shader programs each dedicated to their own corresponding materials? Keeping in mind that the "master shaders" would have to track these additional uniforms and potentially have numerous branches of ifs, it may be possible that the ifs will lead to additional and unnecessary processing. But would that more expensive than constantly calling glUseProgram to switch shaders, or storing the shaders to begin with?
      With all these angles to consider, it's difficult to come to a conclusion. Both possible methods work, and both seem rather convenient for their own reasons, but which is the most performant? Please help this beginner/dummy understand. Thank you!
    • By JJCDeveloper
      I want to make professional java 3d game with server program and database,packet handling for multiplayer and client-server communicating,maps rendering,models,and stuffs Which aspect of java can I learn and where can I learn java Lwjgl OpenGL rendering Like minecraft and world of tanks
    • By AyeRonTarpas
      A friend of mine and I are making a 2D game engine as a learning experience and to hopefully build upon the experience in the long run.

      -What I'm using:
          C++;. Since im learning this language while in college and its one of the popular language to make games with why not.     Visual Studios; Im using a windows so yea.     SDL or GLFW; was thinking about SDL since i do some research on it where it is catching my interest but i hear SDL is a huge package compared to GLFW, so i may do GLFW to start with as learning since i may get overwhelmed with SDL.  
      -Questions
      Knowing what we want in the engine what should our main focus be in terms of learning. File managements, with headers, functions ect. How can i properly manage files with out confusing myself and my friend when sharing code. Alternative to Visual studios: My friend has a mac and cant properly use Vis studios, is there another alternative to it?  
    • By ferreiradaselva
      Both functions are available since 3.0, and I'm currently using `glMapBuffer()`, which works fine.
      But, I was wondering if anyone has experienced advantage in using `glMapBufferRange()`, which allows to specify the range of the mapped buffer. Could this be only a safety measure or does it improve performance?
      Note: I'm not asking about glBufferSubData()/glBufferData. Those two are irrelevant in this case.
    • By xhcao
      Before using void glBindImageTexture(    GLuint unit, GLuint texture, GLint level, GLboolean layered, GLint layer, GLenum access, GLenum format), does need to make sure that texture is completeness. 
  • Popular Now