[maemo-developers] [maemo-developers] Unreliable Large Network Transfers

From: Mike Lococo mpl22 at cornell.edu
Date: Sat Dec 16 04:31:30 EET 2006
Hi Folks,

>> I'm finding that large (>200MB) transfers of data via the wifi network 
>> are extremely unreliable.
> Are you sure network is a problem? Are you writing data somewhere? Both 
> MMC card and iternal flash are really slow when writing.

This is the issue.  I can reproduce both the slow write speed (~150KB/s) 
and the GUI unresponsiveness with (from memory, please forgive any typos):

dd if=/dev/zero of=/media/mmc1/test.file bs=1M count=250

which doesn't involve the network at all.

I may do some playing with multiblock write kernels at this point, 
although it's not so much the (average) speed that's the problem.  I 
think the real issue is that the CPU doesn't seem to be able to service 
requests from other subsystems in a timely manner once the write cache 
fills up.  Userspace programs are getting regularly starved for CPU time 
for several seconds at a time, which causes the wildly fluctuating 
transfer rates, the unresponsive GUI, the Unison sessions dropping, and 
possibly the reboots (as programs aren't responding to the watchdog 

The Unison failures, in particular, are disappointing.  It is such an 
awesome program for syncing the 770 to a desktop system, but if you have 
a large MMC (and you change its contents regularly) it isn't usable at all.


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