From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 10 Sep 2019 10:20:10 -0500 From: David Teigland Message-ID: <20190910152010.GA6789@redhat.com> References: <370ba3fa-53df-7213-8876-d37ef1a3b57e@suse.com> <20190905165519.GB30473@redhat.com> <8b432efdabc3de82146ea6cb87b27c89556bf72e.camel@suse.de> <20190906140351.GB652@redhat.com> <20190909140956.GA31823@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Subject: Re: [linux-lvm] system boot time regression when using lvm2-2.03.05 Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Martin Wilck Cc: LVM general discussion and development , Heming Zhao > > > _pvscan_aa > > > vgchange_activate > > > _activate_lvs_in_vg > > > sync_local_dev_names > > > fs_unlock > > > dm_udev_wait <=== this point! > > > ``` > Could you explain to us what's happening in this code? IIUC, an > incoming uevent triggers pvscan, which then possibly triggers VG > activation. That in turn would create more uevents. The pvscan process > then waits for uevents for the tree "root" of the activated LVs to be > processed. > > Can't we move this waiting logic out of the uevent handling? It seems > weird to me that a process that acts on a uevent waits for the > completion of another, later uevent. This is almost guaranteed to cause > delays during "uevent storms". Is it really necessary? > > Maybe we could create a separate service that would be responsible for > waiting for all these outstanding udev cookies? Peter Rajnoha walked me through the details of this, and explained that a timeout as you describe looks quite possible given default timeouts, and that lvm doesn't really require that udev wait. So, I pushed out this patch to allow pvscan with --noudevsync: https://sourceware.org/git/?p=lvm2.git;a=commitdiff;h=3e5e7fd6c93517278b2451a08f47e16d052babbb You'll want to add that option to lvm2-pvscan.service; we can hopefully update the service to use that if things look good from testing.