Re: [Users] VirtIO disk latency

This is a multi-part message in MIME format. ------=_NextPartTM-000-269ed284-0ba0-45cc-bfe3-0742919cf61b Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable atency=0A= - or 125us latency=0A= d - or 450us latency=0A= =0A= Thanks for taking time to help. =0A= =0A= I have used several tools to measure latencies but it=0A= always boils down to the same numbers. The software =0A= components and their releases should not matter to get =0A= a first overview. The important thing is to ensure that a =0A= read request of a test inside the VM is really passing the =0A= QEMU layer. =0A= =0A= The simplest test I can think of (at least in our case) is to=0A= start a Windows VM and attach a very small NFS disk with=0A= 1GB to it. Start it, install HDTune Trial and run the random =0A= access test to the small disk. Other ways could be to run =0A= some kind of direct IO based read test inside the VM.=0A= =0A= During each test I can see the packets running between =0A= the NFS server and the hypervisor so I know that each=0A= request is not cached inside the VM or QEMU. =0A= =0A= After one or two runs the filecache in the RAM of our NFS =0A= server has all the hot data and latency decreases down to=0A= the microseconds area. With that we can derive the=0A= penalty of the virtualization layer.=0A= =0A= Whatever I try to optimize I only reach 1/4th of the I/Os=0A= of ESX for very small packets (512 bytes or 1K). And=0A= that inside the same (migrated) VM on the same NFS=0A= topology with the same test programs.=0A= =0A= The baseline numbers for the hypervisor are an average of =0A= running direct io based test tools onto files residing on=0A= the same NFS.=0A= =0A= Markus=0A= =0A= P.S. I'm not complaining about that performance. =0A= Driving an IPoIB environment you get used to waste =0A= bandwidth and latency. But it is always good to know=0A= where it comes from.= ------=_NextPartTM-000-269ed284-0ba0-45cc-bfe3-0742919cf61b Content-Type: text/plain; name="InterScan_Disclaimer.txt" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="InterScan_Disclaimer.txt" **************************************************************************** Diese E-Mail enthält vertrauliche und/oder rechtlich geschützte Informationen. Wenn Sie nicht der richtige Adressat sind oder diese E-Mail irrtümlich erhalten haben, informieren Sie bitte sofort den Absender und vernichten Sie diese Mail. Das unerlaubte Kopieren sowie die unbefugte Weitergabe dieser Mail ist nicht gestattet. Über das Internet versandte E-Mails können unter fremden Namen erstellt oder manipuliert werden. Deshalb ist diese als E-Mail verschickte Nachricht keine rechtsverbindliche Willenserklärung. Collogia Unternehmensberatung AG Ubierring 11 D-50678 Köln Vorstand: Kadir Akin Dr. Michael Höhnerbach Vorsitzender des Aufsichtsrates: Hans Kristian Langva Registergericht: Amtsgericht Köln Registernummer: HRB 52 497 This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden. e-mails sent over the internet may have been written under a wrong name or been manipulated. That is why this message sent as an e-mail is not a legally binding declaration of intention. Collogia Unternehmensberatung AG Ubierring 11 D-50678 Köln executive board: Kadir Akin Dr. Michael Höhnerbach President of the supervisory board: Hans Kristian Langva Registry office: district court Cologne Register number: HRB 52 497 **************************************************************************** ------=_NextPartTM-000-269ed284-0ba0-45cc-bfe3-0742919cf61b--