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RE: [lwip-users] Transferring large data fast and pointing pbufsdirectly
From: |
Grubb, Jared |
Subject: |
RE: [lwip-users] Transferring large data fast and pointing pbufsdirectly to Ethernet receive buffers |
Date: |
Wed, 12 Dec 2007 11:50:58 -0800 |
Bill,
If you can describe the way the buffer descriptors and memory allocation
works, maybe there is a way to use 'custom memory pools' to simulate
what you need.
Jared
-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of
Bill Auerbach
Sent: Wednesday, December 12, 2007 11:27
To: 'Mailing list for lwIP users'
Subject: RE: [lwip-users] Transferring large data fast and pointing
pbufsdirectly to Ethernet receive buffers
Hello,
> Just being pedantic I know, but that isn't strictly true - I'm working
on
> one board which can scatter/gather pbufs and where the memory pointed
to
> by the buffer descriptors is fixed at 128 bytes.
I don't think in our case combining fragmented pbuf is going to be our
bottleneck. But we also have the memory to use a larger buffer.
> However if you do have the memory it is more efficient to use the full
> 1516. The question then is whether you have the memory because _every_
> packet received will occupy the full 1516 bytes, and if you're keeping
> them around till you've got the lot, that can add up. If you are
receiving
> your 4MB image in 256 byte chunks, you'd need at least 24MB of RAM ;).
If we are pulling the image while it's coming in, this won't be a
problem.
If the link is faster than we are, this could be. I think we'll be
waiting
on the data, not the data coming in faster than we can handle it.
> NB the value of 1516 bytes can depend on your hardware, e.g. if your
> hardware also transfers the CRCs. See
> http://sd.wareonearth.com/~phil/net/jumbo/ for example.
Thanks - interesting - I'd not looked into Jumbo Frames.
> Just to clarify what Simon is saying, pool pbufs consist of a 'struct
> pbuf' immediately followed in memory by the payload - so if you have
the
> payload pointer, you know where the struct pbuf is.
This does help - thank you.
> Indeed. I've certainly only been working in terms of (inherently
> preallocated) pool pbufs.
I see this is the way to go. I'll have to see if I can figure how to
release the ETH buffer the pbuf points to when the pbuf has been
processed.
Thank you!
Bill
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- Re: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, (continued)
- Re: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, address@hidden, 2007/12/11
- RE: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, Bill Auerbach, 2007/12/12
- Re: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, Jonathan Larmour, 2007/12/12
- RE: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, Bill Auerbach, 2007/12/12
- Re: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, Jonathan Larmour, 2007/12/12
- RE: [lwip-users] Transferring large data fast and pointing pbufsdirectly to Ethernet receive buffers,
Grubb, Jared <=
- RE: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, Bill Auerbach, 2007/12/12
- Re: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, address@hidden, 2007/12/12
- RE: [lwip-users] Transferring large data fast and pointing pbufsdirectly to Ethernet receive buffers, Grubb, Jared, 2007/12/12
- Re: [lwip-users] Transferring large data fast and pointing pbufsdirectly to Ethernet receive buffers, Jonathan Larmour, 2007/12/12
- RE: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, Bill Auerbach, 2007/12/12
- RE: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, Bill Auerbach, 2007/12/12
RE: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers, Bill Auerbach, 2007/12/12