Re: MAXSAVEDBLOCKS in netinet/tcp_sack.c

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

:I'm running TCP experiences between DragonFlyBSD and FreeBSD.
:In my experiences, both send buffer and receive buffer are 4MBytes.
:And RTT is set to 20ms using Dummynet.
:
:In that case, since bandwidth delay product is large, MAXSAVEDBLOCKS
:in netinet/tcp_sack.c is too small to use DragonFlyBSD as a sender.
:I need to change the value from 8 to 128 for my experiences.
:
:So, I'd like to suggest to change the value of MAXSAVEDBLOCKS to
:a larger value.  I also would like to suggest to introduce a new
:sysctl variable to control the maximum number of saved blocks.
:
:Thank you.
:
:Regards,
:Noritoshi Demizu

    This is one for Jeff to consider when he gets back as well.  I do
    like the idea of having a sysctl.

    But I will note that the saved blocks are in fact the number of
    discontiguous segment ranges, not single segments.  That should make it
    fairly independant of the bandwidth delay product on a real network.
    If you use dummynet to inject random errors... well, that isn't really
    a characteristic of a real network.  I still believe that there are
    certain situations where one might need to bump the number up, which
    is why I like the sysctl idea.  I'm not sure the default needs to be
    increased, though.

					-Matt
					Matthew Dillon 
					<dillon@xxxxxxxxxxxxx>