Danilo Godec
2009-Apr-28 13:09 UTC
[Xen-users] IO performance depends on number of DomU''s?
Hi, I was monitoring IO performance of my Xen server using ''iostat'' on Dom0 and ''bonnie++''. With no DomU''s running, I get about 40 MB/s write and 70 MB7s read - which seems OK for a SW RAID5 array with 6 SATA drives... Running only one DomU doesn''t change much - running bonnie++ on either Dom0 or DomU shows almost the same result (again monitoring ''iostat'' on Dom0). After I start 16 DomU''s, the IO performance goes down the drain - I only get 5-6 MB/s running bonnie++ in Dom0 - or any of the DomU''s. What''s interesting is that ''iostat'' on Dom0 also shows only 5-6 MB/s of IO - so it doesn''t look like the cumulative IO of all DomU''s would saturate the actual IO capability of the hardware... Any ideas? Things to try? Is it possible to dedicate one of the CPUs to Dom0 exclusively? Danilo _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Robert Dunkley
2009-Apr-28 13:22 UTC
RE: [Xen-users] IO performance depends on number of DomU''s?
Is it possible to dedicate one of the CPUs to Dom0 exclusively? Yes. Add this to the kernel boot line: dom0_max_vcpus=1 Edit /etc/xen/xend-config.sxp - set “(dom0-cpus 1)” Reboot Dom0 Regards, Rob -----Original Message----- From: xen-users-bounces@lists.xensource.com [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of Danilo Godec Sent: 28 April 2009 14:09 To: xen-users@lists.xensource.com Subject: [Xen-users] IO performance depends on number of DomU''s? Hi, I was monitoring IO performance of my Xen server using ''iostat'' on Dom0 and ''bonnie++''. With no DomU''s running, I get about 40 MB/s write and 70 MB7s read - which seems OK for a SW RAID5 array with 6 SATA drives... Running only one DomU doesn''t change much - running bonnie++ on either Dom0 or DomU shows almost the same result (again monitoring ''iostat'' on Dom0). After I start 16 DomU''s, the IO performance goes down the drain - I only get 5-6 MB/s running bonnie++ in Dom0 - or any of the DomU''s. What''s interesting is that ''iostat'' on Dom0 also shows only 5-6 MB/s of IO - so it doesn''t look like the cumulative IO of all DomU''s would saturate the actual IO capability of the hardware... Any ideas? Things to try? Is it possible to dedicate one of the CPUs to Dom0 exclusively? Danilo _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users The SAQ Group Registered Office: 18 Chapel Street, Petersfield, Hampshire GU32 3DZ SAQ is the trading name of SEMTEC Limited. Registered in England & Wales Company Number: 06481952 http://www.saqnet.co.uk AS29219 SAQ Group Delivers high quality, honestly priced communication and I.T. services to UK Business. Broadband : Domains : Email : Hosting : CoLo : Servers : Racks : Transit : Backups : Managed Networks : Remote Support. ISPA Member Find us in http://www.thebestof.co.uk/petersfield _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Fajar A. Nugraha
2009-Apr-28 13:31 UTC
Re: [Xen-users] IO performance depends on number of DomU''s?
On Tue, Apr 28, 2009 at 8:22 PM, Robert Dunkley <Robert@saq.co.uk> wrote:> Is it possible to dedicate one of the CPUs to Dom0 exclusively? > > Yes. > Add this to the kernel boot line: dom0_max_vcpus=1 > Edit /etc/xen/xend-config.sxp - set “(dom0-cpus 1)” > Reboot Dom0Some additional info : - you might also want this line on kernel boot line :dom0_vcpus_pin. This would ensure that dom0''s vcpu 0 (the active one if it only uses one vcpu) is assigned on physical cpu 0 (or core 0 on multicore system). - those steps does not actually dedicate one CPU to dom0 exclusively. What it does is it LIMITS dom0 to only use one CPU. To assign it exclusively, you also need to tell domUs to NOT use that particular CPU. Something like ''cpus="1-7"'' (for 8-core system) on domU config would tell it to NOT use core 0.However since current xen scheduler is smart enough to assign cpu dynamically you might see the same result with only the above config if your system load is low enough. - to achive the same effect on your current session only without the need to reboot: xm vcpu-set 0 1 xm vcpu-pin 0 0 0 Regards, Fajar _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Olivier B.
2009-Apr-28 13:36 UTC
Re: [Xen-users] IO performance depends on number of DomU''s?
Hi, is it always usefull if irqbalance is installed on Dom0 ? Or maybe irqbalance is not usefull at all with Xen ? Olivier Fajar A. Nugraha a écrit :> On Tue, Apr 28, 2009 at 8:22 PM, Robert Dunkley <Robert@saq.co.uk> wrote: > >> Is it possible to dedicate one of the CPUs to Dom0 exclusively? >> >> Yes. >> Add this to the kernel boot line: dom0_max_vcpus=1 >> Edit /etc/xen/xend-config.sxp - set “(dom0-cpus 1)” >> Reboot Dom0 >> > > Some additional info : > - you might also want this line on kernel boot line :dom0_vcpus_pin. > This would ensure that dom0''s vcpu 0 (the active one if it only uses > one vcpu) is assigned on physical cpu 0 (or core 0 on multicore > system). > - those steps does not actually dedicate one CPU to dom0 exclusively. > What it does is it LIMITS dom0 to only use one CPU. To assign it > exclusively, you also need to tell domUs to NOT use that particular > CPU. Something like ''cpus="1-7"'' (for 8-core system) on domU config > would tell it to NOT use core 0.However since current xen scheduler is > smart enough to assign cpu dynamically you might see the same result > with only the above config if your system load is low enough. > - to achive the same effect on your current session only without the > need to reboot: > xm vcpu-set 0 1 > xm vcpu-pin 0 0 0 > > Regards, > > Fajar > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users