From: David Teigland <teigland@redhat.com>
To: Martin Wilck <martin.wilck@suse.com>
Cc: "zkabelac@redhat.com" <zkabelac@redhat.com>,
"bmarzins@redhat.com" <bmarzins@redhat.com>,
"prajnoha@redhat.com" <prajnoha@redhat.com>,
"linux-lvm@redhat.com" <linux-lvm@redhat.com>,
Heming Zhao <heming.zhao@suse.com>
Subject: Re: [linux-lvm] Discussion: performance issue on event activation mode
Date: Thu, 30 Sep 2021 09:26:29 -0500 [thread overview]
Message-ID: <20210930142629.GA32174@redhat.com> (raw)
In-Reply-To: <700af71c5293946105c779dbf9e8cd95344fc7af.camel@suse.com>
On Thu, Sep 30, 2021 at 07:22:29AM +0000, Martin Wilck wrote:
> On Wed, 2021-09-29 at 23:39 +0200, Peter Rajnoha wrote:
> > For event-based activation, I'd expect it to really behave in event-
> > based manner, that is, to respond to events as soon as they come and not
> > wait for all the other devices unnecessarily.
>
> I may be missing something here. Perhaps I misunderstood David's
> concept. Of course event-based activation is best - in theory.
> The reason we're having this discussion is that it may cause thousands
> of event handlers being executed in parallel, and that we have seen
> cases where this was causing the system to stall during boot for
> minutes, or even forever. The ideal solution for that would be to
> figure out how to avoid the contention, but I thought you and David had
> given up on that.
>
> Heming has shown that the "static" activation didn't suffer from this
> problem. So, to my understanding, David was seeking for a way to
> reconcile these two concepts, by starting out statically and switching
> to event-based activation when we can without the risk of stalling. To
> do that, we must figure out when to switch, and (like it or not) udev
> settle is the best indicator we have.
>
> Also IMO David was striving for a solution that "just works"
> efficiently both an small and big systems, without the admin having to
> adjust configuration files.
Right, this is not entirely event based any longer, so there could be some
advantage of an event-based system that we sacrifice. I think that will
be a good tradeoff for the large majority of cases, and will make a good
default.
> > The use of udev-settle is always a pain - for example, if there's a mount
> > point defined on top of an LV, with udev-settle as dependency, we practically
> > wait for all devices to settle. With 'all', I mean even devices which are not
> > block devices and which are not event related to any of that LVM
> > layout and the stack underneath. So simply we could be waiting uselessly and we
> > could increase possibility of a timeout (...for the mount point etc.).
One theoretical advantage of an event-based system is that it reacts
immediately, so you get faster results. In practice it's often anything
but immediate, largely because of extra work and moving parts in the
event-based scheme, processing each event individually. So, the simpler
non-event-based method will often be faster I think, and more robust (all
the moving parts are where things break, so best to minimize them.)
You've filled in some interesting details about udev-settle for me, and it
sounds like there are some ideas forming about an alternative, which would
offer us a better way to switch to event-base-mode. I'd like to be able
to simply replace the systemd-udev-settle dependency with an improved
"new-settle" dependency when that's ready.
Dave
_______________________________________________
linux-lvm mailing list
linux-lvm@redhat.com
https://listman.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
next prev parent reply other threads:[~2021-09-30 14:27 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210930142629.GA32174@redhat.com \
--to=teigland@redhat.com \
--cc=bmarzins@redhat.com \
--cc=heming.zhao@suse.com \
--cc=linux-lvm@redhat.com \
--cc=martin.wilck@suse.com \
--cc=prajnoha@redhat.com \
--cc=zkabelac@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).