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

From: Kimmo Hämäläinen kimmo.hamalainen at nokia.com
Date: Mon Dec 18 14:01:50 EET 2006
On Fri, 2006-12-15 at 21:31 -0500, ext Mike Lococo wrote:
> 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

I asked around and there seems to be a known kernel problem with this,
but there's a workaround: it should work if you use 4k block size.

BR, Kimmo

> 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 
> promptly?).
> 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.
> Thanks,
> Mike
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