From: David Teigland <teigland@redhat.com>
To: Peter Rajnoha <prajnoha@redhat.com>
Cc: zkabelac@redhat.com, bmarzins@redhat.com, martin.wilck@suse.com,
heming.zhao@suse.com, linux-lvm@redhat.com
Subject: Re: [linux-lvm] Discussion: performance issue on event activation mode
Date: Mon, 27 Sep 2021 10:38:22 -0500 [thread overview]
Message-ID: <20210927153822.GA4779@redhat.com> (raw)
In-Reply-To: <20210927100032.xczilyd5263b4ohk@alatyr-rpi.brq.redhat.com>
On Mon, Sep 27, 2021 at 12:00:32PM +0200, Peter Rajnoha wrote:
> > - We could use the new lvm-activate-* services to replace the activation
> > generator when lvm.conf event_activation=0. This would be done by simply
> > not creating the event-activation-on file when event_activation=0.
>
> ...the issue I see here is around the systemd-udev-settle:
Thanks, I have a couple questions about the udev-settle to understand that
better, although it seems we may not need it.
> - the setup where lvm-activate-vgs*.service are always there (not
> generated only on event_activation=0 as it was before with the
> original lvm2-activation-*.service) practically means we always
> make a dependency on systemd-udev-settle.service, which we shouldn't
> do in case we have event_activation=1.
Why wouldn't the event_activation=1 case want a dependency on udev-settle?
> - If we want to make sure that we run our "non-event-based activation"
> after systemd-udev-settle.service, we also need to use
> "After=systemd-udev-settle.service" (the "Wants" will only make the
> udev settle service executed, but it doesn't order it with respect
> to our activation services, so it can happen in parallel - we want
> it to happen after the udev settle).
So we may not fully benefit from settling unless we use After (although
the benefits are uncertain as mentioned below.)
> Now the question is whether we really need the systemd-udev-settle at
> all, even for that non-event-based lvm activation. The udev-settle is
> just to make sure that all the udev processing and udev db content is
> complete for all triggered devices. But if we're not reading udev db and
> we're OK that those devices might be open in parallel to lvm activation
> period (e.g. because there's blkid scan done on disks/PVs), we should be
> OK even without that settle. However, we're reading some info from udev db,
> right? (like the multipath component state etc.)
- Reading the udev db: with the default external_device_info_source=none
we no longer ask the udev db for any info about devs. (We now follow
that setting strictly, and only ask udev when source=udev.)
- Concurrent blkid and activation: I can't find an issue with this
(couldn't force any interference with some quick tests.)
- I wonder if After=udev-settle could have an incidental but meaningful
effect of more PVs being in place before the service runs?
I'll try dropping udev-settle in all cases to see how things look.
Dave
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next prev parent reply other threads:[~2021-09-27 15:39 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-06 6:15 [linux-lvm] Discussion: performance issue on event activation mode heming.zhao
2021-06-06 16:35 ` Roger Heflin
2021-06-07 10:27 ` Martin Wilck
2021-06-07 15:30 ` heming.zhao
2021-06-07 15:45 ` Martin Wilck
2021-06-07 20:52 ` Roger Heflin
2021-06-07 21:30 ` David Teigland
2021-06-08 8:26 ` Martin Wilck
2021-06-08 15:39 ` David Teigland
2021-06-08 15:47 ` Martin Wilck
2021-06-08 16:02 ` Zdenek Kabelac
2021-06-08 16:05 ` Martin Wilck
2021-06-08 16:03 ` David Teigland
2021-06-08 16:07 ` Martin Wilck
2021-06-15 17:03 ` David Teigland
2021-06-15 18:21 ` Zdenek Kabelac
2021-06-16 16:18 ` heming.zhao
2021-06-16 16:38 ` David Teigland
2021-06-17 3:46 ` heming.zhao
2021-06-17 15:27 ` David Teigland
2021-06-08 16:49 ` heming.zhao
2021-06-08 16:18 ` heming.zhao
2021-06-09 4:01 ` heming.zhao
2021-06-09 5:37 ` Heming Zhao
2021-06-09 18:59 ` David Teigland
2021-06-10 17:23 ` heming.zhao
2021-06-07 15:48 ` Martin Wilck
2021-06-07 16:31 ` Zdenek Kabelac
2021-06-07 21:48 ` David Teigland
2021-06-08 12:29 ` Peter Rajnoha
2021-06-08 13:23 ` Martin Wilck
2021-06-08 13:41 ` Peter Rajnoha
2021-06-08 13:46 ` Zdenek Kabelac
2021-06-08 13:56 ` Peter Rajnoha
2021-06-08 14:23 ` Zdenek Kabelac
2021-06-08 14:48 ` Martin Wilck
2021-06-08 15:19 ` Peter Rajnoha
2021-06-08 15:39 ` Martin Wilck
2021-09-09 19:44 ` David Teigland
2021-09-10 17:38 ` Martin Wilck
2021-09-12 16:51 ` heming.zhao
2021-09-27 10:00 ` Peter Rajnoha
2021-09-27 15:38 ` David Teigland [this message]
2021-09-28 6:34 ` Martin Wilck
2021-09-28 14:42 ` David Teigland
2021-09-28 15:16 ` Martin Wilck
2021-09-28 15:31 ` Martin Wilck
2021-09-28 15:56 ` David Teigland
2021-09-28 18:03 ` Benjamin Marzinski
2021-09-28 17:42 ` Benjamin Marzinski
2021-09-28 19:15 ` Martin Wilck
2021-09-29 22:06 ` Peter Rajnoha
2021-09-30 7:51 ` Martin Wilck
2021-09-30 8:07 ` heming.zhao
2021-09-30 9:31 ` Martin Wilck
2021-09-30 11:41 ` Peter Rajnoha
2021-09-30 15:32 ` heming.zhao
2021-10-01 7:41 ` Martin Wilck
2021-10-01 8:08 ` Peter Rajnoha
2021-09-30 11:29 ` Peter Rajnoha
2021-09-30 16:04 ` David Teigland
2021-09-30 14:41 ` Benjamin Marzinski
2021-10-01 7:42 ` Martin Wilck
2021-09-29 21:53 ` Peter Rajnoha
2021-09-30 7:45 ` Martin Wilck
2021-09-29 21:39 ` Peter Rajnoha
2021-09-30 7:22 ` Martin Wilck
2021-09-30 14:26 ` David Teigland
2021-09-30 15:55 ` David Teigland
2021-10-01 8:00 ` Peter Rajnoha
2021-10-18 6:24 ` Martin Wilck
2021-10-18 15:04 ` David Teigland
2021-10-18 16:56 ` heming.zhao
2021-10-18 21:51 ` Zdenek Kabelac
2021-10-19 17:18 ` David Teigland
2021-10-20 14:40 ` Martin Wilck
2021-10-20 14:50 ` David Teigland
2021-10-20 14:54 ` Martin Wilck
2021-10-20 15:12 ` David Teigland
2021-06-07 16:40 ` David Teigland
2021-07-02 21:09 ` David Teigland
2021-07-02 21:22 ` Martin Wilck
2021-07-02 22:02 ` David Teigland
2021-07-03 11:49 ` heming.zhao
2021-07-08 10:10 ` Tom Yan
2021-07-02 21:31 ` Tom Yan
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