Re: Packet loss every 30.999 seconds

On Fri, 28 Dec 2007, Bruce Evans wrote:

In previous mail, you (Mark) wrote:

# With FreeBSD 4 I was able to run a UDP data collector with rtprio set,
# kern.ipc.maxsockbuf=20480000, then use setsockopt() with SO_RCVBUF
# in the application. If packets were dropped they would show up
# with netstat -s as "dropped due to full socket buffers".
# # Since the packet never makes it to ip_input() I no longer have
# any way to count drops. There will always be corner cases where
# interrupts are lost and drops not accounted for if the adapter
# hardware can't report them, but right now I've got no way to
# estimate any loss.

I tried using SO_RCVBUF in ttcp (it's an old version of ttcp that doesn't
have an option for this). With the default kern.ipc.maxsockbuf of 256K,
this didn't seem to help. 20MB should work better :-) but I didn't try that.

I've now tried this. With kern.ipc.maxsockbuf=20480000 (~20MB) an
SO_RCVBUF of 0x1000000 (16MB), the "socket buffer full lossage increases
from ~300 kpps (~47%) to ~450 kpps (70%) with tiny packets. I think
this is caused by most accesses to the larger buffer being cache misses
-- since the system can't keep up, cache misses make it worse).

However, with 1500-byte packets, the larger buffer reduces the lossage
from 1 kpps in 76 kpps to precisely zero pps, at a cost of only a small
percentage of system overhead (~20Idle to ~18%Idle).

The above is with net.isr.direct=1. With net.isr.direct=0, the loss is
too small to be obvious and is reported as 0, but I don't trust the
report. ttcp's packet counts indicate losses of a few per million with
direct=0 but none with direct=1. "while :; do sync; sleep 0.1" in the
background causes a loss of about 100 pps with direct=0 and a smaller
loss with direct=1. Running the ttcp receiver at rtprio 0 doesn't make
much difference to the losses.

Bruce
_______________________________________________
freebsd-net@xxxxxxxxxxx mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-net
To unsubscribe, send any mail to "freebsd-net-unsubscribe@xxxxxxxxxxx"

Relevant Pages

  • Re: Packet loss every 30.999 seconds
    ... # With FreeBSD 4 I was able to run a UDP data collector with rtprio set, ... the "socket buffer full lossage increases ... However, with 1500-byte packets, the larger buffer reduces the lossage ... With net.isr.direct=0, the loss is ...
    (freebsd-stable)
  • Re: Losing UDP packets with MFC Sockets
    ... The usual way to reduce UDP packet loss is to favor smaller and more ... frequent packets over larger and infrequent packets. ... size and increase the receive buffer size. ...
    (microsoft.public.vc.mfc)
  • Re: In-tree version of new FireWire drivers available
    ... Just to recap, the dual buffer receive mode, as described in section ... quadlet aligned amount of header data can be appended into one buffer ... *either* the header buffer or the payload buffer fills up. ... enough to hold headers for all the packets it takes to fill up the ...
    (Linux-Kernel)
  • Re: Waveform Audio - MMSYSERR_INVALPARAM
    ... Also, packets/buffers that you waveOutWrite, are packets ... right after the last sample from the previous buffer seamlessly. ... the waveOutWrite function DON'T return the error. ...
    (microsoft.public.pocketpc.developer)
  • Re: Persistent stall in the Cypress FX2 FIFO
    ... the FX2's firmware code, would be to install some sort of stub routines ... > how long they are (it appends even for 4 byte long packets). ... > a packet from the FIFO before sending the next one all works fine... ... smaller or larger than what a single buffer could hold. ...
    (comp.arch.embedded)