Hi, On Wed, 24 Oct 2012, Marcy Cortes wrote: > Hello listers, > > We've hit a pretty nasty bug in SLES 11 SP2 kernel at 3.0.34 and higher. > Basically the I/O goes crazy - like 4000-6000 i/o per sec - and the server > becomes unresponsive. It's highly creatable by running a WebSphere deploy or > starting WMB sw. SuSE says there is a bug in cfq and the work around for > now is to set elevator=deadline in the kernel parameters. This does seem to > mitigate the problem. > > It's got me wondering though what is the current recommendation is for z on > ECKD DS8700. This doc > http://doc.opensuse.org/products/draft/SLES/SLES-tuning_sd_draft/cha.tuning.io.html > says "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). Trying to query with cat /sys/block/dasd*/queue/scheduler > comes back always with [deadline] being the default, even if elevator= isn't > specified in the parms. Is there another way to query it? > > This IBM presentation seems to indicate that deadline is the default on z > (but maybe it's not now as of kernel 3.0.34?) > http://people.redhat.com/bhinson/pdfs/BestPractices_IBM.pdf > > > And some older doc seems to indicate that noop is the best choice with > intelligent disk subsystems like DS8xxx. > > Any insight would be most helpful!
The default IO scheduler for SLES11SP2 on z is deadline (set during compile time via CONFIG_DEFAULT_IOSCHED). You can overwrite this at IPL time via the elevator= kernel parameter. The DASD driver does not use the default but always sets deadline at block device creation time. To query the IO scheduler per block device read from /sys/block/<bdev>/queue/scheduler or with a current userspace via "lsblk -t". You can change the scheduler per block device at runtime by writing to /sys/block/<bdev>/queue/scheduler. Regards, Sebastian ---------------------------------------------------------------------- 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/
