And more questions before I get an answer to the last one :) If we're going to go changing it to all to deadline, is that the best choice?
I see that many folks recommend noop for KVM virtual machines, wouldn't this also apply under z? And Oracle mentions noop here http://www.zseriesoraclesig.org/2012presentations/2012_226_simpson_11gR2CustExpSys_z_pptV2.pdf as a way to reduce CPU consumption, although databases aren't your average i/o kind of guys either of course. I found this in an old xSeries redbook of all places http://www.redbooks.ibm.com/redpapers/pdfs/redp3861.pdf Select the right I/O elevator in kernel 2.6 For most server workloads, the complete fair queuing (CFQ) elevator is an adequate choice as it is optimized for the multiuser, multiprocess environment a typical server operates in. However, certain environments can benefit from a different I/O elevator. Intelligent disk subsystems Benchmarks have shown that the NOOP elevator is an interesting alternative in high-end server environments. When using IBM ServeRAID or TotalStorage DS class disk subsystems, the lack of ordering capability of the NOOP elevator becomes its strength. Intelligent disk subsystems such as IBM ServeRAID and TotalStorage DS class disk subsystems feature their own I/O ordering capabilities. Enterprise class disk subsystems may contain multiple SCSI or FibreChannel disks that each have individual disk heads and data striped across the disks. It would be very difficult for an operating system to anticipate the I/O characteristics of such complex subsystems correctly, so you might often observe at least equal performance at less overhead when using the NOOP I/O elevator. Virtual machines Virtual machines, regardless of whether in VMware or VM for zSeries(r), may only communicate through the virtualization layer with the underlying hardware. Hence a virtual machine is not aware of the fact if the assigned disk device consists of a single SCSI device or an array of FibreChannel disks on a TotalStorage DS8000. The virtualization layer takes care of necessary I/O reordering and the communication with the physical block devices. Therefore, we recommend using the NOOP elevator for virtual machines to ensure minimal processor overhead. Marcy Cortes Operating Systems Engineer, z/VM and Linux on System z Compute Platform Services, Mainframe/Midrange Services Wells Fargo Bank | MAC A0194-110 | San Francisco Cell 415-517-0895 [email protected] This message may contain confidential and/or privileged information. If you are not the addressee or authorized to receive this for the addressee, you must not use, copy, disclose, or take any action based on this message or any information herein. If you have received this message in error, please advise the sender immediately by reply e-mail and delete this message. Thank you for your cooperation. -----Original Message----- From: Cortes, Marcy D. Sent: Thursday, October 25, 2012 9:19 AM To: [email protected] Subject: RE: [LINUX-390] I/O scheduler on sles 11 sp2 on z Yes! We are using LVM extensively. So cfq is being used on LVM by default then? Marcy This message may contain confidential and/or privileged information. If you are not the addressee or authorized to receive this for the addressee, you must not use, copy, disclose, or take any action based on this message or any information herein. If you have received this message in error, please advise the sender immediately by reply e-mail and delete this message. Thank you for your cooperation. -----Original Message----- From: Linux on 390 Port [mailto:[email protected]] On Behalf Of Peter Oberparleiter Sent: Thursday, October 25, 2012 12:55 AM To: [email protected] Subject: Re: [LINUX-390] I/O scheduler on sles 11 sp2 on z On 24.10.2012 18:54, Marcy Cortes wrote: > "On IBM System z the default I/O scheduler for a storage device is set by the > device driver", but trying to query what it is seems to indicate that > everything is deadline already (but it must not be or the parm wouldn't have > helped). Could it be that you are using LVM which adds its own block devices which are not affected by DASD's elevator defaults? Regards, Peter Oberparleiter -- Peter Oberparleiter Linux on System z Development - IBM Germany ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/ ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
