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

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Date:   Sun, 25 Mar 2018 09:41:31 +0200
From:   Paul Menzel <pmenzel+linux-efi@...gen.mpg.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: efisubsys_init takes more than a few milliseconds

Dear Ard,


Thank you for the quick reply.


On 03/24/2018 11:35 PM, Ard Biesheuvel wrote:

> On 24 March 2018 at 22:10, Paul Menzel <pmenzel+linux-efi@...gen.mpg.de> wrote:
>> Dear Ard,
>>
>>
>> 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
```

>> To reproduce this, clone the pm-graph repository [2], use `sudo
>> ./bootgraph.py -f -fstat -maxdepth 10 -manual` to see what to add to
>> `/boot/grub/grub.cfg`. Then reboot, and execute `sudo ./bootgraph.py -f
>> -fstat -maxdepth 10`.
>>
>> If your system is powerful enough, you can use a higher maximum depth. I
>> didn’t get around how `-cgfilter` works to get smaller HTML files.


Kind regards,

Paul


>> [1] https://01.org/suspendresume
>> [2] https://github.com/01org/pm-graph