[linux-lvm] Discussion: performance issue on event activation mode
tom.ty89 at gmail.com
Fri Jul 2 21:31:09 UTC 2021
On Sat, 3 Jul 2021 at 05:17, David Teigland <teigland at redhat.com> wrote:
> On Sun, Jun 06, 2021 at 02:15:23PM +0800, heming.zhao at suse.com wrote:
> > dev_cache_scan //order: O(n^2)
> > + _insert_dirs //O(n)
> > | if obtain_device_list_from_udev() true
> > | _insert_udev_dir //O(n)
> > |
> > + dev_cache_index_devs //O(n)
> I've been running some experiments and trying some patches to improve
> this. By setting obtain_device_list_from_udev=0, and using the attached
> patch to disable dev_cache_index_devs, the pvscan is much better.
> systemctl status lvm2-pvscan appears to show that the pvscan command
> itself runs for only 2-4 seconds, while the service as a whole takes
> around 15 seconds. See the 16 sec gap below from the end of pvscan
> to the systemd Started message. If that's accurate, the remaining delay
> would lie outside lvm.
Not necessarily. It could be pvscan stalling for 16s after printing
the "now active" message for some reason before exiting (with 0).
> Jul 02 15:27:57 localhost.localdomain systemd: Starting LVM event activation on device 253:1710...
> Jul 02 15:28:00 localhost.localdomain lvm: pvscan PV /dev/mapper/mpathalz online, VG 1ed02c7d-0019-43c4-91b5-f220f3521ba9 is complete.
> Jul 02 15:28:00 localhost.localdomain lvm: pvscan VG 1ed02c7d-0019-43c4-91b5-f220f3521ba9 run autoactivation.
> Jul 02 15:28:00 localhost.localdomain lvm: 1 logical volume(s) in volume group "1ed02c7d-0019-43c4-91b5-f220f3521ba9" now active
> Jul 02 15:28:16 localhost.localdomain systemd: Started LVM event activation on device 253:1710.
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