Scatter-gather NIC

[sanjayk]

hi all
I have a query regarding the scatter-gather support available in
network interface cards.
What exactly is meant by scatter-gather?
Does it means reading or writing data from mulitple locations
simultaneously by the NIC.

Also which all popular n/w cards supports this facility
specially does epro100 driver has this feature

TIA
sanjayk

[Thekkedath Gopakumar-agt026]

Post by sanjayk
What exactly is meant by scatter-gather?
Does it means reading or writing data from mulitple locations
simultaneously by the NIC.

One of the constraints in DMA is that the physical memory buffer sould be
contiguous.
A device with scatter gather capability allows the programmer to allocate
many buffers
(each of which is contiguous of course) at various memory locations for DMA.
For example,
in a network card, the driver writer can have many software buffers intented
to hold say packets
received by the device. The device knows the starting address of each of
these buffers (how to feed
this addresses to the device is device dependent) and on receiving a packet
will DMA it to the next available
buffer.



<http://clients.rediff.com/signature/track_sig.asp>

[Arun Prasad Velu]

It's a capability substantially enhance Large I/O request performance, if
they are supported by the hardware.

Scatter reading is the ability to deliver data blocks stored at consecutive
hardware address to non-consecutive memory addresses.

Gather writing is the ability to deliver blocks of date stored at
non-consecutive memory addresses to consecutively addressed hardware blocks.

This concept is primarily used in the Hard Disks .

-----Original Message-----
From: kernelnewbies-***@nl.linux.org
[mailto:kernelnewbies-***@nl.linux.org]On Behalf Of Thekkedath
Gopakumar-agt026
Sent: Friday, January 21, 2005 9:19 AM
To: sanjayk; ***@nl.linux.org
Subject: RE: Scatter-gather NIC

Post by sanjayk
What exactly is meant by scatter-gather?
Does it means reading or writing data from mulitple locations
simultaneously by the NIC.

One of the constraints in DMA is that the physical memory buffer sould be
contiguous.
A device with scatter gather capability allows the programmer to allocate
many buffers
(each of which is contiguous of course) at various memory locations for DMA.
For example,
in a network card, the driver writer can have many software buffers intented
to hold say packets
received by the device. The device knows the starting address of each of
these buffers (how to feed
this addresses to the device is device dependent) and on receiving a packet
will DMA it to the next available
buffer.






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