Re: [linux-lvm] Discussion: performance issue on event activation mode

[David Teigland <teigland@redhat.com>]

On Thu, Jun 17, 2021 at 12:18:47AM +0800, heming.zhao@suse.com wrote:
> I don't know if I missed something, the result didn't show any progress.
> the result of "devices/obtain_device_list_from_udev=0" even got regression: from 23.3 => 39.8
> 
> the lvm2 version with dev-dct-device-info-1 branch code
> ```
> sle15sp2-base40g:~ # lvm version
>   LVM version:     2.03.13(2)-git (2021-05-07)
>   Library version: 1.02.179-git (2021-05-07)
>   Driver version:  4.40.0
>   Configuration:   ./configure --host=x86_64-suse-linux-gnu --build=x86_64-suse-linux-gnu --program-prefix= --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64 --libexecdir=/usr/lib --localstatedir=/var --sharedstatedir=/var/lib --mandir=/usr/share/man --infodir=/usr/share/info --disable-dependency-tracking --enable-dmeventd --enable-cmdlib --enable-udev_rules --enable-udev_sync --with-udev-prefix=/usr/ --enable-selinux --enable-pkgconfig --with-usrlibdir=/usr/lib64 --with-usrsbindir=/usr/sbin --with-default-dm-run-dir=/run --with-tmpfilesdir=/usr/lib/tmpfiles.d --with-thin=internal --with-device-gid=6 --with-device-mode=0640 --with-device-uid=0 --with-dmeventd-path=/usr/sbin/dmeventd --with-thin-check=/usr/sbin/thin_check --with-thin-dump=/usr/sbin/thin_dump --with-thin-repair=/usr/sbin/thin_repair --enable-blkid_wiping --enable-lvmpolld --enable-re
 altime --with-cache=internal --with-default-locking-dir=/run/lock/lvm --with-default-pid-dir=/run --with-default-run-dir=/run/lvm --enable-fsadm --disable-silent-rules --enable-write_install --with-vdo=none
> ```
> 
> Installation with cmd: make install && dracut -f --add "lvm"
> 
> top 10 blame services
> ```
> external_device_info_source = "none"
> obtain_device_list_from_udev = 1
> event_activation = 1
> udev_sync = 1

Thanks for running that again.  From your previous testing, my conclusion
was that libudev caused the slowdown.  So, the patch is supposed to avoid
all libudev calls by default, and rely only on lvm's native device type
detection.  The default settings to avoid libudev, are:

  obtain_device_list_from_udev = 0
  external_device_info_source = "none"

I'm not sure which of your test results match those settings, but if those
results are not improved, then we should look further to see if the
slowdown is caused by something other than libudev calls.

Dave

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