DragonFly kernel List (threaded) for 2005-07
:I made another experiences and found that, if HZ is increased, the
:throughput is improved. Note that bandwidth=100Mbit/s=12.5Mbyte/s
:and RTT=20ms in my experimental environment. Here are results of
:time to send 512KB data without losses.
Yes, I would expect this, but I am not going to go the same route
that FreeBSD has gone where a high HZ is required for the system to
The bandwidth estimation works with any HZ value, but it takes a lot
longer to get a good estimate when HZ is low simply because the
granularity of the measurement is far higher. But, again, this
particular case is only testing short transfers. I believe this issue
can be solved with initial conditions. Probably not with the patch
I enclosed earlier (it's too unstable at the beginning of a transfer).
Probably with something stored in the route table.
:As a result, if one uses BDP limiting, I think 1/HZ should be set to
:much smaller value than RTT.
No, we definitely are not going to do this. First, it's impossible
to scale the value to the network because, frankly, the network can
be anything from a PPP connection over a serial port to a 10GigE
link. Secondly, it's a bad idea to make subsystems dependant on
the system's base tick being 'fast'.
We could tune the system to make BDP work perfectly in your test
environment, but it would skew the parameters too much relative to
other things the system does. e.g. the scheduler would become much
less efficient, and system overheads would increase (significantly at
10,000 hz which would only be 100uS per interrupt).