Re: Variable download speed

On Tue, 23 Feb 2016, Neal Cardwell wrote:

On Tue, Feb 23, 2016 at 8:57 AM,  [off-list ref] wrote:

quoted

I published example pcap file under following link:

https://www.dropbox.com/s/v8375ub16seyt1a/test7.pcap?dl=0

I hope it is possible to download it without creating dropbox account.

Thanks for the trace. It looks like for the first 0.8 seconds of the
trace some non-TCP component on the receiving machine (app, CPU, CPU
power-saving mechanisms, NIC, or NIC driver) is limiting throughput to
78Mbit/sec (e.g. the very first window of 10 packets is ACKed at that
rate). Then the throughput increases to over 200 Mbit/sec. AFAICT it
doesn't look like the TCP layer is doing anything wrong. I'd look for
issues with those other components. It might help to report the
receiver application, receiver CPU type, kernel version, NIC, and NIC
driver.

Hi,

The receiver application was "wget" using ftp protocol.
Linux kernel is in version 3.4.11-rt19.

Concerning hardware I have not much information about it.
Everything I've got is:

- CPU: ARMv7 Processor rev 1 (v7l)
- NIC: Broadcom PCI: 14e4:aa52
- RAM: 256MB

Unfortunately I've no much info about kernel. Seems like it is some kind 
of realtime version. Can this realtime extension cause such effect of 
increasing throughput?


I've made a graph with window size and throughput from published 
test7.pcap file:

https://www.dropbox.com/s/cwars3oaoax73fh/wget_test_test7pcap_20160224_1.png?dl=0


sdrb