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Tue, 8 Jun 2021 15:39:48 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8E03F60CC6; Tue, 8 Jun 2021 15:39:46 +0000 (UTC) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id 79D721800BB4; Tue, 8 Jun 2021 15:39:41 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id 158FddEH016867 for ; Tue, 8 Jun 2021 11:39:39 -0400 Received: by smtp.corp.redhat.com (Postfix) id 74B8D19D9D; Tue, 8 Jun 2021 15:39:39 +0000 (UTC) Received: from redhat.com (null.msp.redhat.com [10.15.80.136]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D63DE19C45; Tue, 8 Jun 2021 15:39:38 +0000 (UTC) Date: Tue, 8 Jun 2021 10:39:37 -0500 From: David Teigland To: Martin Wilck Message-ID: <20210608153937.GA21355@redhat.com> References: <20210607213003.GA8181@redhat.com> <1760ea9715bc7a16d4efe10dd95105d663a07228.camel@suse.com> MIME-Version: 1.0 In-Reply-To: <1760ea9715bc7a16d4efe10dd95105d663a07228.camel@suse.com> User-Agent: Mutt/1.8.3 (2017-05-23) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-loop: linux-lvm@redhat.com Cc: "rogerheflin@gmail.com" , "zkabelac@redhat.com" , prajnoha@redhat.com, Heming Zhao , "linux-lvm@redhat.com" Subject: Re: [linux-lvm] Discussion: performance issue on event activation mode X-BeenThere: linux-lvm@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-lvm-bounces@redhat.com Errors-To: linux-lvm-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=linux-lvm-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 _______________________________________________ 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/