--On Monday, August 25, 2008 07:51:37 PM +0200 Harald Barth <[EMAIL PROTECTED]>
wrote:
As '-nojumbo' has a measurable price on our own local network where
fragmentation does not exhibit any problem we hesitate to run
everything in that mode.
I run with -nojumbo and with RX_MAX_FRAG patched to 1.
On which clients/servers do you see that this would have a performance
penalty?
Last time I checked on Linux there was no difference in letting the RX
code produce 4 UDP packets a ~1400 bytes which then are as many
eternet frames compared to let RX produce 1 packet a ~5600 bytes and
then the OS fragment it into 4 ethernet packets. Yes, there was a
difference back in the days of SunOS 4.1.4....
There is a significant difference, because if the OS fragments the packet,
then all four fragments must make it to the other end in order for anything
to be received. If any of the fragments is dropped (say, due to network
congestion) then the entire packet (all four fragments) needs to be
retransmitted. This sort of behavior makes congestion worse, and is why
path MTU discovery is so important.
-- Jeff
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