Re: [RFC] Why Xorg waits for long time(200ms+) to invoke VT_RELDISP?

[Yu Chen]

Hi Adam,
thanks for your reply,
On Wed, Dec 7, 2016 at 2:17 AM, Adam Jackson  wrote:
> On Thu, 2016-11-17 at 14:18 +0800, Yu Chen wrote:
>
>> May I know why Xorg takes 200ms+ before acking with VT_RELDISP?
>
> Because it's been asked to set the hardware back to text mode, which
> requires reprogramming the GPU, which takes time.
>
> 200ms is more time than it probably _should_ take, but you haven't
> specified (either in this email or in the bug you link to) what GPU
> this is and which driver you're using, so I can't be any more specific
> about what exactly is taking so much time and how it can be avoided
> without that.
The GPU is：
00:02.0 VGA compatible controller: Intel Corporation Broadwell-U
Integrated Graphics (rev 09) (prog-if 00 [VGA controller])
Subsystem: Apple Inc. Broadwell-U Integrated Graphics
driver in use: i915
Xorg version:
X.Org X Server 1.18.3
Release Date: 2016-04-04

thanks,
Yu
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Re: [RFC] Why Xorg waits for long time(200ms+) to invoke VT_RELDISP?

[Adam Jackson]

On Thu, 2016-11-17 at 14:18 +0800, Yu Chen wrote:

> May I know why Xorg takes 200ms+ before acking with VT_RELDISP?

Because it's been asked to set the hardware back to text mode, which
requires reprogramming the GPU, which takes time.

200ms is more time than it probably _should_ take, but you haven't
specified (either in this email or in the bug you link to) what GPU
this is and which driver you're using, so I can't be any more specific
about what exactly is taking so much time and how it can be avoided
without that.

- ajax
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[RFC] Why Xorg waits for long time(200ms+) to invoke VT_RELDISP?

[Yu Chen]

Hi all,
Currently I'm evaluating the suspend/resume speed on my laptop,
and it was found the switching from Graphic Mode to text mode vt has taken more
than 200ms, and according to the ftrace result, after Xorg received
the signal from kernel, it waits for 200ms+ until finally issue the
ioctl VT_RELDISP, which makes the kernel blocking at this flag to be
set.
May I know why Xorg takes 200ms+ before acking with VT_RELDISP?
Thanks very much.

More info please refer to:
https://bugzilla.kernel.org/show_bug.cgi?id=186211

thanks,
Yu
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