Re: [PATCH] ALSA: hda: Request driver probe from an async task

[Paul Menzel]

Dear Takashi,


On 04/23/18 14:21, Takashi Iwai wrote:
> On Mon, 23 Apr 2018 14:05:52 +0200,
> Paul Menzel wrote:
> > From: Paul Menzel <pmenzel@xxxxxxxxxxxxx>
> > Date: Sat, 24 Mar 2018 09:28:43 +0100
> >
> > On an ASRock E350M1, with Linux 4.17-rc1 according to `initcall_debug`
> > calling `azx_driver_init` takes sometimes more than a few milliseconds,
> > and up to 200 ms.
> >
> > ```
> > [    2.892598] calling  azx_driver_init+0x0/0xfe4 [snd_hda_intel] @ 218
> > [    2.943002] initcall azx_driver_init+0x0/0xfe4 [snd_hda_intel]
> > returned 0 after 49195 usecs
> > ```
> >
> > Trying to execute the Linux kernel in less than 500 ms, this is quite a
> > hold-up, and therefore request the probe from an async task.
> >
> > With this change, the test shows, that the function returns earlier.
> >
> > ```
> > [    3.254800] calling  azx_driver_init+0x0/0xfe4 [snd_hda_intel] @ 227
> > [    3.254887] initcall azx_driver_init+0x0/0xfe4 [snd_hda_intel]
> > returned 0 after 66 usecs
> > ```
> >
> > The same behavior is visible on a Dell OptiPlex 7010. The longer times
> > seem to happen, when the module *e1000e* is probed during the same time.
> >
> > Signed-off-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx>
>
> What actually took so long?  Could you analyze further instead of
> blindly putting the flag?

Well, I am not sure. Could you please give me hints, how to debug this 
further? Is there some debug flag?

I am only aware of the Ftrace framework, but in my experience it also 
skews the timings quite a bit, so might not be the best choice.


Kind regards,

Paul

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