From: David Teigland <teigland@redhat.com>
To: Martin Wilck <martin.wilck@suse.com>
Cc: "rogerheflin@gmail.com" <rogerheflin@gmail.com>,
"zkabelac@redhat.com" <zkabelac@redhat.com>,
prajnoha@redhat.com, Heming Zhao <heming.zhao@suse.com>,
"linux-lvm@redhat.com" <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] Discussion: performance issue on event activation mode
Date: Tue, 8 Jun 2021 10:39:37 -0500 [thread overview]
Message-ID: <20210608153937.GA21355@redhat.com> (raw)
In-Reply-To: <1760ea9715bc7a16d4efe10dd95105d663a07228.camel@suse.com>
On Tue, Jun 08, 2021 at 08:26:01AM +0000, Martin Wilck wrote:
> IIUC, 2) is the effect of _pvscan_aa_quick(). 3) is surprising;
> apparently libudev's device detection causes a factor 3 slowdown.
> While 40s is not bad, you can see that event based activation still
> performs far worse than "serial" device detection lvm2-activation-
> early.service.
>
> Personally, I'm sort of wary about obtain_device_list_from_udev=0
> because I'm uncertain whether it might break multipath/MD detection.
> Perhaps you can clarify that.
Yes, that's an issue, but it's something we've needed to clean up for a
while, and I made a small start on it a while back.
obtain_device_list_from_udev is supposed to only control whether lvm gets
a list of device names from readdir /dev, or from libudev. My preference
is default 0, readdir /dev. This avoids the performance problem and makes
lvm less dependent on the vagaries of udev in general.
But, as you and Peter mentioned, obtain_device_list_from_udev also became
entangled with md/mpath detection methods, which is more closely related
to external_device_info_source=udev|none.
I think it would be an improvement to:
. Make obtain_device_list_from_udev only control how we get the device
list. Then we can easily default to 0 and readdir /dev if it's better.
. Use both native md/mpath detection *and* udev info when it's readily
available (don't wait for it), instead of limiting ourselves to one
source of info. If either source indicates an md/mpath component,
then we consider it true.
The second point means we are free to change obtain_device_list_from_udev
as we wish, without affecting md/mpath detection. It may also improve
md/mpath detection overall.
A third related improvement that could follow is to add stronger native
mpath detection, in which lvm uses uses /etc/multipath/wwids, directly or
through a multipath library, to identify mpath components. This would
supplement the existing sysfs and udev sources, and address the difficult
case where the mpath device is not yet set up.
Dave
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next prev parent reply other threads:[~2021-06-08 15:40 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 [this message]
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
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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