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Fri, 01 Oct 2021 09:41:32 +0200 X-MC-Unique: hy2CzCCsPCuI8Iso7FjyYA-1 Received: from DB8PR04MB6555.eurprd04.prod.outlook.com (2603:10a6:10:103::20) by DBBPR04MB7580.eurprd04.prod.outlook.com (2603:10a6:10:1f7::9) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4566.15; Fri, 1 Oct 2021 07:41:32 +0000 Received: from DB8PR04MB6555.eurprd04.prod.outlook.com ([fe80::5158:3113:295b:d9c1]) by DB8PR04MB6555.eurprd04.prod.outlook.com ([fe80::5158:3113:295b:d9c1%5]) with mapi id 15.20.4566.015; Fri, 1 Oct 2021 07:41:32 +0000 From: Martin Wilck To: "linux-lvm@redhat.com" , "prajnoha@redhat.com" Thread-Topic: [linux-lvm] Discussion: performance issue on event activation mode Thread-Index: AQHXWptdVb+iQI7pP06gMwUhQri0uKsIs+kAgABkm4CAAPX+gIAADzyAgJKTMYCAG6beAIAAXmQAgAD6QwCAAIiSAIAACUiAgAAo+QCAAdwggIAAoz0AgAAElwCAADusAIAAQJOAgAEOzgA= Date: Fri, 1 Oct 2021 07:41:31 +0000 Message-ID: <074e7d61fac100ef3bdb49edb2a29b4b6a666ef3.camel@suse.com> References: <20210607214835.GB8181@redhat.com> <20210608122901.o7nw3v56kt756acu@alatyr-rpi.brq.redhat.com> <20210909194417.GC19437@redhat.com> <20210927100032.xczilyd5263b4ohk@alatyr-rpi.brq.redhat.com> <20210927153822.GA4779@redhat.com> <9947152f39a9c5663abdbe3dfee343556e8d53d7.camel@suse.com> <20210928144254.GC11549@redhat.com> <138b7ddb721b6a58df8f0401b76c7975678f0dda.camel@suse.com> <20210928174246.GF3087@octiron.msp.redhat.com> <20210929220653.p45cvgzdhlbnp4gy@alatyr-rpi.brq.redhat.com> <7e91a1e8-2379-a33c-1482-b31adaa7bc8b@suse.com> In-Reply-To: <7e91a1e8-2379-a33c-1482-b31adaa7bc8b@suse.com> Accept-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: user-agent: Evolution 3.40.4 x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: a3fdd0ba-cd9a-4c51-73da-08d984aee331 x-ms-traffictypediagnostic: DBBPR04MB7580: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:7691 x-ms-exchange-senderadcheck: 1 x-ms-exchange-antispam-relay: 0 x-microsoft-antispam: BCL:0 x-microsoft-antispam-message-info: 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 x-forefront-antispam-report: CIP:255.255.255.255; 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Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-MIME-Autoconverted: from quoted-printable to 8bit by lists01.pubmisc.prod.ext.phx2.redhat.com id 1917fbDd012317 X-loop: linux-lvm@redhat.com X-Mailman-Approved-At: Fri, 01 Oct 2021 04:09:17 -0400 Cc: "bmarzins@redhat.com" , "teigland@redhat.com" , "zkabelac@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 2.84 on 10.5.11.23 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-Language: en-US Content-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Thu, 2021-09-30 at 23:32 +0800, heming.zhao@suse.com wrote: > > I just want to say that some of the issues might simply be > > regressions/issues with systemd/udev that could be fixed. We as > > providers of block device abstractions where we need to handle, > > sometimes, thousands of devices, might be the first ones to hit these > > issues. > > > > The rhel8 callgrind picture > (https://prajnoha.fedorapeople.org/bz1986158/rhel8_libudev_critical_cost.png > ) > responds to my analysis: > https://listman.redhat.com/archives/linux-lvm/2021-June/msg00022.html > handle_db_line took too much time and become the hotspot. I missed that post. You wrote > the dev_cache_scan doesn't have direct disk IOs, but libudev will scan/read > udev db which issue real disk IOs (location is /run/udev/data). > ... > 2. scans/reads udev db (/run/udev/data). may O(n) > udev will call device_read_db => handle_db_line to handle every > line of a db file. > ... > I didn't test the related udev code, and guess the <2> takes too much time. ... but note that /run/udev is on tmpfs, not on a real disk. So the accesses should be very fast unless there's some locking happening. Regards Martin _______________________________________________ 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/