Re: Strange IO behaviour on wakeup from sleep

[Zachary Amsden <zach@vmware.com>]

>
>
>Hi !
>
>Not much datas at this point yet, but paulus and I noticed that current
>bk (happened already last saturday or so) has a very strange problem
>when waking up from sleep (suspend to ram) on our laptops.
>
>This doesn't seem to be directly related to the PM code, at least not
>the arch one, as far as I know. The IDE throughput goes down to less
>than 100k/sec on hdparm. We haven't yet figured out where the time is
>lost, the disk seem to properly be restored to UDMA4 as usual, that code
>didn't change for ages, I don't think it's a problem at that level in
>IDE.
>  
>

I would tend to be very suspicious of DMA not being restored correctly 
because on some systems, prior to or during suspend, DMA may be shutdown 
to conserve power.  There are changes afloat that touch suspend/resume, 
and there have been historical problems with DMA not being restored 
properly after wakeup on some laptops.

Although this may be another shot in the dark, it might rule out the DMA 
problem:  try cat /proc/ide/yourchipset before and after suspend and 
note any changes.  Failing that, use hdparm to turn off DMA before 
suspend and see if the performance suffers to the same degree as after 
wakeup.

Zachary Amsden
zach@vmware.com