[Intel-gfx] Suggestions on fixing fill_modes ioctl() delays under i915

Dan Aloni alonid at gmail.com
Mon Apr 16 17:54:32 CEST 2012

On Mon, Apr 16, 2012 at 4:33 PM, Eugeni Dodonov <eugeni at dodonov.net> wrote:

> On Mon, Apr 16, 2012 at 09:04, Dan Aloni <alonid at gmail.com> wrote:
>> Hello,
>> I'd like to assist in fixing an issue that is quite nagging concerning
>> the i915 driver. I wasn't sure whether to classify this as a bug, but it's
>> something worth considering. Let me explain.
>> When I first used the i915 driver on my Lenovo X220 laptop, I noticed
>> that every time I run xrandr, or when any X client tries to query the
>> display modes, the X server hangs for a second or so. Using systemtap, I
>> was able to track the hang to the Intel DRM driver, around the area in
>> which it talks over i2C in order to query the modes from display controller.
> Could you try using the 3.4-rc1 or newer kernel by a chance? The patch
> that I initially sent in past October which improves the i2c interaction
> for output detection over 'phantom' outputs went in there, and so far it
> seems to improve the display detection timing by 30%-3000% (depending on
> hardware of course and number of outputs and such).

Okay, with 3.4-rc3 I can confirm that it works much better. For the xrandr
test case, I've timed each ioctl to about 60 milli-secs with 9 calls
spanning over half a second. Any further suggestions? Isn't it possible to
tell that nothing is connected and then not try to probe those ports at all?
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