netdev - Question: How to configure the Ethernet receive buffer allocation (was: (no subject)).

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Date:	Sat, 13 Oct 2012 10:39:27 +0200
From:	Ronny Meeus <ronny.meeus@...il.com>
To:	netdev <netdev@...r.kernel.org>
Subject: Question: How to configure the Ethernet receive buffer allocation
 (was: (no subject)).

Hello

I have an application that needs to handle a massive amount of
Ethernet packets coming from an FPGA on a dedicated Ethernet link.
I use a raw Ethernet socket for this. By increasing the receive buffer
of the socket, I'm able to capture all the packets and process them in
the application. Since this processing can take some time I have
increased the receive buffer to 500Mb. The size of the packets is
1000bytes so I'm able to capture 500k packets.

What I observe is that the kernel allocates buffers from the
slaballoctor for these packets but it takes buffers of 4k while in
fact the packet is only 1k (This means 2G of kernel memory  is being
used).
Is it possible to fine-tune this or is that an alternative for this?

I already investigated the PACKET_RX_RING solution. This has the
advantage that the buffers can be 1k but  I do not want to consume
500Mb of virtual memory in my application which is running on MIPS in
32 bit mode where I only have 2G available in user space.

---
Ronny
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