Re: efisubsys_init takes more than a few milliseconds
From: Paul Menzel
Date: Sun Mar 25 2018 - 03:41:44 EST
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@xxxxxxxxxxxxx> 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).
```
[â]
[ 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
[â]
```
To get a vanilla Linux kernel to boot in well under one second, itâd 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
doesnât respond to these kind of reports, as they think, itâs 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.
Thatâd be great.
In the mean time, you can try passing 'efi=noruntime' to the kernel.
Thank you, I didnât 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
didnât 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