[Libdlo] defio mmap issues

Justin Hammond justin at dynam.ac
Tue May 25 21:20:18 PDT 2010

Hi Bernie,
Thanks for the heads up. I'll do some testing and see how it goes.


On 26-May-2010, at 3:50 AM, Bernie Thompson <bernie at plugable.com> wrote:

> Just an update on this problem (detail below) of horizontal artifacts
> with defio enabled in udlfb, and then using a standard (non-damage
> aware) mmap client like the generic fbdev X server ....
> Others ran across these same problems in a different (non-DisplayLink)
> context, and are working on a fix.  I've not tested these patches to
> defio yet, but they may resolve this issue
> http://marc.info/?l=linux-fbdev&m=127369791432181
> Note: There's some further discussion on the list, so this is likely
> not the final patch they'll run with.  But it's great that there
> appears to be a fix on the horizon for this.
> Best wishes,
> Bernie
> http://plugable.com/
> On Wed, Jan 13, 2010 at 4:36 PM, Bernie Thompson  
> <bernie at plugable.com> wrote:
>> On Mon, Jan 11, 2010 at 6:57 AM, <justin at dynam.ac> wrote:
>>> On a side note, and maybe for a latter email, I'm also getting  
>>> horizontal
>>> artifacts on the screen after several hours of operations. Reading  
>>> the
>>> archives, I saw someone else post on this, and there was a thought  
>>> there
>>> was a race condition on the memmap. This is very reproducible for me
>>> (takes about 1 hour though) so if I can provide further info to  
>>> help debug
>>> that, I'm willing to take on the challenge!
>> Here are some datapoints from trying to track down this issue:
>> * The problem happens both with the latest udlfb from git.plugable.com 
>> , and
>> with jaya's original defio driver patch posted a few months back.  
>> So it
>> could be a problem carried forward, but it doesn't look like a new  
>> problem
>> ..
>> * It can be seen more frequently with faster processors and larger  
>> screens.
>> On my atom with 1920x1080, it's intermittent and small corruption.   
>> On a
>> faster Celeron with 3 1680x1050 screens, it starts happening  
>> quickly with
>> any significant screen activity.
>> * And a fun one: on that multi-screen setup, once you get large  
>> areas of the
>> one screen (one DL device) to fail to render ... then moving the  
>> mouse and
>> triggering rendering on the *other* DL device/screen, for the  
>> corresponding
>> lines on the screen, refreshes the first device/screen properly  
>> (!)  Since
>> udlfb keeps no shared state between different DisplayLink devices,
>> apparently this confusion is happening at the defio/vma/page table  
>> level.
>> Defio is used by several other framebuffer drivers, but perhaps not  
>> at these
>> resolutions and not for multiple screens.  Has anyone seen other  
>> evidence
>> that would support/contradict this being a general defio problem?  Or
>> perhaps something simple/stupid that udlfb is doing to trigger it?
>> Thanks,
>> Bernie

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