slacer
Posts: 32
Joined: Mon Dec 26, 2011 9:13 am

Re: GPU with shared video memory?

Sun Jan 15, 2012 3:51 pm

Maybe things have changed over time, but I remember that it was always a good advise to stay away from notebooks with without dedicated memory for the graphic card in regard to video/gaming performance.

I have not found information about additional video RAM on the raspberry pi board, so it should be a kind of shared memory for cpu/gpu.

The gpu allows hardware accelerated OpenGL, but where is the memory for textures, vertices, etc. ?

Where should I search for these kind of information for raspberry pi?

Michael

Prometheus
Posts: 308
Joined: Tue Dec 13, 2011 11:09 pm

Re: GPU with shared video memory?

Sun Jan 15, 2012 3:54 pm

I don't know where to search for it, but I gather from posts I've seen that it is indeed shared with the main RAM, and that on a Model B this apparently leaves about 192MB free.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: GPU with shared video memory?

Sun Jan 15, 2012 3:56 pm

Well, searching the forums here is the best start.

The memory is shared between the GPU and Arm. At boot it is partiitioned, some allocated to the GPU, the rest to the Arm and its memory manager. The Arm memory manager is a typical virtual memory thing (standard Arm), the GPU uses a flat address space, so to move data from one to the other requires a certain amount of mmap'ing.

So there is a total memory (128 or 256), allocated between the two devices.
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slacer
Posts: 32
Joined: Mon Dec 26, 2011 9:13 am

Re: GPU with shared video memory?

Sun Jan 15, 2012 5:02 pm

Referring to the forum search feature is a nice start, but it seems there are many posts which point to threads which don't exist any more.

I used the search function within the forum and google, but I did not find a posting about raspberry pi, OpenGL, shared memory and its effect on 3D graphics performance.

This is something I want to check on the device once it is on my desk.

Thank you for the info

PhilS
Posts: 39
Joined: Thu Jan 05, 2012 4:12 pm
Contact: Website

Re: GPU with shared video memory?

Sun Jan 15, 2012 6:04 pm

Prometheus said:


I don't know where to search for it, but I gather from posts I've seen that it is indeed shared with the main RAM, and that on a Model B this apparently leaves about 192MB free.


It'd be nice to know exactly how much the GPU uses, if it is 64MB like you say, that only leaves 64MB on the model A!

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 24942
Joined: Sat Jul 30, 2011 7:41 pm

Re: GPU with shared video memory?

Sun Jan 15, 2012 8:14 pm

PhilS said:


Prometheus said:


I don't know where to search for it, but I gather from posts I've seen that it is indeed shared with the main RAM, and that on a Model B this apparently leaves about 192MB free.


It'd be nice to know exactly how much the GPU uses, if it is 64MB like you say, that only leaves 64MB on the model A!


Technically, you can divide it how how you want. Not sure how you do that from a users perspective (I'll try and find out). It all depends on what you want the GPU to do. In general, and not using a camera, its pretty low in memory requirements. If you have a high megapixel camera, you need to give the GPU more memory, but to be honest, you need to go to pretty high MP's to use over 64 and that's triple buffering and recording 1080p30 H264 a the same time.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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