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

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Message-ID: <1350124173.21172.14017.camel@edumazet-glaptop>
Date:	Sat, 13 Oct 2012 12:29:33 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ronny Meeus <ronny.meeus@...il.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: Question: How to configure the Ethernet receive buffer
 allocation (was: (no subject)).

On Sat, 2012-10-13 at 12:14 +0200, Ronny Meeus wrote:

> The ideal solution would be to have a solution were we use a packet
> ring to store the packets in but use a standard socket to receive the
> packets from this ring. In this way we can combine the ideal memory
> usage of the packet ring solution (in fact almost no overhead)
> combined with the virtual memory that must not be wasted in the
> application space.
> 
> I have no clue whether this is possible ...

But how do you know before receiving packet from network that its size
will be 1000 instead of 1500 ?

Packet ring is nice when you have the right size, or else you need to
add a copy of packets. Or you dedicate an ethernet device for an
application (direct delivery to user land, no skbs at all)

2.6.32 kernel is a bit old for us on netdev.

If you try latest kernel (Linus tree), you'll discover we no longer use
one kmalloc-4096 entry to store a packet.

However, with MTU=1500, we still consume around 2048 bytes per packet
(including overhead)

If you really cant change packet size and stay at 1000, you could try :
reducing device mtu, to lower wasted ram per packet

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