Date: Wed, 17 Jul 2002 22:26:06 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Luigi Rizzo <rizzo@icir.org> Cc: Mike Silbersack <silby@silby.com>, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/netinet tcp_timer.h Message-ID: <200207180526.g6I5Q6ND015937@apollo.backplane.com> References: <20020717220320.F83856-100000@patrocles.silby.com> <200207180445.g6I4jkD4006497@apollo.backplane.com> <20020717220630.A17698@iguana.icir.org>
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:as someone mentioned, one big source of variability in RTT measurements
:are delayed acks, which depend on the other side.
Delayed acks should have no effect whatsoever. The transmitter
should 'P'ush the last data block and this should cause the
receiver to ack it immediately. In a continuous stream of data an ack
is required to occur at least once every two packets.
:I think that it is nice to be able to control the min. timeout,
:but you should put it into a sysctl variable, and use a very
:conservative value (200...1000)ms as default.
I am working up a patch set to be able to set the minimum rtt
and a slop value that is added after the rtt calculation (so
it applies to everything, not just the minimum). I still think
200ms is too much. How about 50ms?
:You can handle it in a way similar to sched_quantum, so you read/write
:it in terms of fractions of second but the internal value is stored
:in ticks, and you can apply some consistency checks on the values
:passed by userland. What is the point of recomputing hz/50 all the times?
:
:just a side comment -- "polling issues" are resolved within 1 tick, but
:1 tick on the sender side, so local HZ values do not count.
:
: cheers
: luigi
Right. There are already a number of TCP variables, like mss setting.
I'll just use the same sysctl conversion format. I think it's in
milliseconds.
-Matt
Matthew Dillon
<dillon@backplane.com>
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