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

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Date:   Mon, 23 Apr 2018 14:30:36 +0200
From:   Paul Menzel <pmenzel+alsa-devel@...gen.mpg.de>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: hda: Request driver probe from an async task

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@...gen.mpg.de>
>> 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@...gen.mpg.de>
> 
> 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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