[asterisk-dev] nVidia Cuda

Mon Mar 5 09:33:11 MST 2007

You can certain read  more about it in the cuda doc. Anyway, to sum it
up simply. There are 16 independent "multi-processors" in the g80
running internally at the speed of 1.2GHz, and each "multi-processor"
contain 8 "processors". These 8 processors has to run in lock steps on
their respective data. In other words, there is only one instruction
decode and one execution unit across those 8 processors. However, each
one operates on it own data. So in the worst case, that's when the data
costs the code to diverge, the efficiency of the 8 processors will be
reduced (depending on how badly diverge the code is writen) as if there
is only one processor. So, even in the worst case, and given 35mhz per
channcel, we can still expect the G80 to  handle (a bit conservertive
here) 20 (per multi-processor 1.2GHz/35MHz) * 16 = 320, which is still
vey impressive. Just to put things into perspective, a board from Aculab
that can deliever than kind of performance costs $14,000 USD.

-----Original Message-----
From: asterisk-dev-bounces at lists.digium.com
[mailto:asterisk-dev-bounces at lists.digium.com] On Behalf Of CA DM
Sent: Monday, March 05, 2007 11:04 AM
To: Asterisk Developers Mailing List
Subject: RE: [asterisk-dev] nVidia Cuda

It's possible to assign a single stream processor of G80 to a precise
Asterisk channel. G80 have A LOT of stream processors (ranging from
64 to 128 channels, depending on the GPU).

Can be a very simple way of using GPUs, cutting down from code the need
to have an arbiter that assigns jobs to the stream processor dinamically
(a single stream processor is assumed to be "locked" to an Asterisck
channel).

Cesare

At 16.27 05/03/2007, you wrote:
>Someone once told me that g729 talkes 35mhz per channel. GPU wasting 
>cycles is not a concern since when the GPU is waiting for the cpu to 
>complete it tast, the GPU can take on other tasts or doing 
>transformation for other channels. This is exactly why I think the GPU 
>is perfect for Asterisk type of system. I are not trying to speed up 
>coding/decoding here, but rather, doing it for all channels at the same

>time. As a matter of fact, if one has a 3ghz cpu, transcoding can be 
>done faster on the cpu than the g80 is the code is a straight port.
>
>-----Original Message-----
>From: asterisk-dev-bounces at lists.digium.com
>[mailto:asterisk-dev-bounces at lists.digium.com] On Behalf Of Matthew 
>Rubenstein
>Sent: Monday, March 05, 2007 8:32 AM
>To: CA DM
>Cc: Asterisk-Dev
>Subject: Re: [asterisk-dev] nVidia Cuda
>
>         Do you know the relative MIPS consumed by G.729 in each of the

>decoding and the transformation phases? If the decoding is a 
>significant percentage, then it will block the CPU process while the 
>GPU waits a long time. While a really fast GPU can afford to waste 
>cycles in inefficient logic if it's still faster than the CPU.
>
>
>On Mon, 2007-03-05 at 09:13 +0100, CA DM wrote:
> > You don't need to port the entire codec code to a GPU. GPU aren't 
> > good
>
> > general purpose processors, such as CPU aren't good stream
processors.
> >
> > Code need to be cleaverly distributed across the specific abilities 
> > of
>
> > CPU and GPU (eg.: decoding and unpacking the data stream is a task 
> > suited for the CPU, like data block transformations are for the GPU)

> > if you want to get the most from both.
> >
> > At 20.38 04/03/2007, you wrote:
> > >         Compression algorithms have generally not been ported to 
> > >GPUs like the G80. They're usually more logic and branch oriented 
> > >than just brute force multiply-accumulates that GPUs specialize in.

> > >I
>
> > >also haven't seen any of the popular Asterisk codecs, like G.729 or

> > >GSM, ported to any GPU. Is there a source for codecs ported to
GPUs?
> > >Or any research showing a good approach?
> > >
> > >
> > >On Sun, 2007-03-04 at 10:12 -0700,
> > >asterisk-dev-request at lists.digium.com
> > >wrote:
> > > > Date: Sat, 03 Mar 2007 22:05:19 -0500
> > > > From: Wai Wu <wkwu at calltrol.com>
> > > > Subject: [asterisk-dev] nVidia Cuda
> > > > To: asterisk-dev at lists.digium.com
> > > > Message-ID:
> > > > <B0430B20D208514CB2AFF57E81645C3101B970 at k3-1.Calltrol.com>
> > > > Content-Type: text/plain; charset="iso-8859-1"
> > > >
> > > > Hi devs,
> > > >
> > > > Has any one looked into cuda to see if cpu intensive part of 
> > > > asterisk(like codecs and conference) can be moved to the G80 
> > > > processor? I found that the GF8800 cards are very inexpensive 
> > > > (around 400 USDs per). I have ported some of our financial 
> > > > applications to this board and found almost 10x performance 
> > > > improvement over the 3GHz C2D host processor. I would like to do
>the same for asterisk.
> > > >
> > > > To start. I have been looking into the asterisk code and have no

> > > > crew how it is structured except the addon applications. Here I 
> > > > have two questions.
> > > >
> > > > 1) Is each channel use their own thread if a codec is used?
> > > > 2) Which part of the asterisk code actually makes the call to 
> > > > the necessary codec? I notice in the applications. They save and

> > > > set the frame format, then read from the channel. So I trace the

> > > > read function, but all it does is reading from a file 
> > > > descriptor. So I need some help here.
> > >--
> > >
> > >(C) Matthew Rubenstein
> > >
> > >_______________________________________________
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> >
>--
>
>(C) Matthew Rubenstein
>
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