Re: How to verify RX checksum offload??
Re: How to verify RX checksum offload??
- Subject: Re: How to verify RX checksum offload??
- From: Andrew Gallatin <email@hidden>
- Date: Tue, 07 Jul 2009 14:22:45 -0400
Terry Lambert wrote:
> If receive checksum offloading is enabled then the hardware will reject
> the packet when it sees the bad checksum and the OS will not get to see
> it in the first place. That is more or less the point of checksum
> offloading, to avoid the bus transfer of the copy of the received data
> from the Ethernet chip FIFO into mbufs and the subsequent receive
> interrupt, running the ISR, running ip_input and tcp_input, etc., only
> to have wasted all that work on a bad packet.
Avoiding the transfer of the rare (1 in a million? 100 million?
billion?) packets that are corrupt is not the point of checksum
offloading. The point of checksum offloading is to avoid the OS
needlessly reading the entire packet into memory to verify the
checksum, and thereby polluting its cache.
Drew
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