Re: [PATCH 2/2] grub2: use stat instead of udevadm for partition lookup

[Petr Vorel]

Hi Michael,

> On Tue, Jul 13, 2021 at 12:52:12PM +0200, Petr Vorel wrote:
> > Hi Paul,

> > > Dear Petr, dear Jeff,


> > > Am 08.07.21 um 17:55 schrieb Petr Vorel:
> > > > From: Jeff Mahoney <jeffm@suse.com>

> > > > sysfs_partition_path calls udevadm to resolve the sysfs path for
> > > > a block device. That can be accomplished by stating the device node
> > > > and using the major/minor to follow the symlinks in /sys/dev/block/.

> > > > This cuts the execution time of grub2-mkconfig from 10s to 2s on
> > > > my system.

> > > Petr, where you able to reproduce this issue?
> > No, I'm sorry, I haven't even tried, because accessing sysfs seems to me as 
> > a
> > quickest way anyway. But agree that we drag this patch in opensuse from 2017
> > (for 2.02~rc1), it might not be relevant for nowadays systems.

> > > Could the specifications of Jeff’s system be added to the commit message?
> > Jeff, Michael, could you verify if it's still relevant?

> It is still relevant per my test, although not as considerable as Jeff's
> system.

> I was using openSUSE Tumbleweed, pretty much all defaults and simple,
> btrfs as root file system without any abstraction disks (lvm, mdadm and
> encryption).

>  NAME MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
>  sr0   11:0    1  663M  0 rom  
>  vda  253:0    0   20G  0 disk 
>  vda1 253:1    0  1.4G  0 part [SWAP]
>  vda2 253:2    0 18.6G  0 part /

> The output of `time grub2-mkconfig -o /boot/grub2/grub.cfg` with the
> patch applied.

>  real    0m1.292s
>  user    0m0.782s
>  sys     0m0.427s

> and without

>  real    0m2.323s
>  user    0m1.295s
>  sys     0m0.956s

> This cuts the execution to somewhere near 55%, which is pretty signifcant.

Thanks a lot for testing. I'll send v2 shortly.

> Please note if testing on lvm, there wouldn't have difference on the
> execution time as libdevmapper is used instead of udevadm to get the
> partition start.
Good to know (some of my system have lvm).

Kind regards,
Petr

> Thanks,
> Michael