linux-kernel - Re: efisubsys_init takes more than a few milliseconds

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Date:   Mon, 26 Mar 2018 10:23:38 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Paul Menzel <pmenzel+linux-efi@...gen.mpg.de>
Cc:     linux-efi@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: efisubsys_init takes more than a few milliseconds

On 25 March 2018 at 16:21, Paul Menzel <pmenzel+linux-efi@...gen.mpg.de> wrote:
> Dear Ard,
>
>
> On 03/25/2018 09:41 AM, Paul Menzel wrote:
>
>> On 03/24/2018 11:35 PM, Ard Biesheuvel wrote:
>>
>>> On 24 March 2018 at 22:10, Paul Menzel wrote:
>
>
>>>> According to `initcall_debug`, `efisubsys_init` takes more than a few
>>>> milliseconds to execute on a Dell XPS 13 9370 (Intel(R) Core(TM)
>>>> i7-8550U CPU @ 1.80GHz).
>>>>
>>>>> ```
>>>>> […]
>>>>> [ 0.144474] calling  efisubsys_init+0x0/0x2cf @ 1
>>>>> [ 0.144474] Registered efivars operations
>>>>> [ 0.173690] initcall efisubsys_init+0x0/0x2cf returned 0 after 27343
>>>>> usecs
>>>>> […]
>>>>> ```
>>>>
>>>>
>>>>
>>>> To get a vanilla Linux kernel to boot in well under one second, it’d be
>>>> nice
>>>> if the time could be improved. Do you know, why it takes so long?
>>>>
>>>> According to `bootgraph.py` from pm-graph [1][2] it takes even a little
>>>> longer.
>>>>
>>>>> efisubsys_init: start=690.841, end=720.493, length(w/o overhead)=31.250
>>>>> ms, return=0
>>>>
>>>>
>>>> There are several dozen calls to `virt_efi_get_next_variable()` all but
>>>> one
>>>> taking around 0.335 ms. This path needs to be optimized. Is that
>>>> possible?
>>>
>>>
>>> That depends. These are firmware calls, so to make these calls faster,
>>> you need to modify the firmware, not the kernel.
>>
>>
>> Yeah, unfortunately, no free firmware runs on this laptop, and Dell
>> doesn’t respond to these kind of reports, as they think, it’s not important.
>>
>>> We may be able to make more intrusive changes to get rid of this
>>> delay, e.g., spin up a special kernel thread, but I'd have to check in
>>> more detail.
>>
>>
>> That’d be great.
>>
>>> In the mean time, you can try passing 'efi=noruntime' to the kernel.
>>
>>
>> Thank you, I didn’t know about that. Unfortunately, initcall_debug still
>> reports the same time although the one message is gone.
>>
>> ```
>> $ sudo dmesg | grep efisubsys
>> [    0.145779] calling  efisubsys_init+0x0/0x2cf @ 1
>> [    0.172034] initcall efisubsys_init+0x0/0x2cf returned 0 after 27343
>> usecs
>> ```
>
>
> Hmm, it looks like, I only edited `/etc/default/grub` and didn’t run `sudo
> update-grub`.
>
> ```
> $ sudo dmesg | grep efisubsys
> [ 0.776339] calling  efisubsys_init+0x0/0x2cf @ 1
> [ 0.776339] initcall efisubsys_init+0x0/0x2cf returned 0 after 0 usecs
>
> ```
>

Excellent! If you want it any faster than that, I can't really help you :-)