On Fri, Mar 12, 2021 at 04:35:43PM -0500, Mark Post wrote: > On 3/12/21 3:53 PM, Ted Rodriguez-Bell wrote: > > Yesterday Suse issued an s390-tools patch for SLES 12SP5 that does this: > > > > * Changing the scheduler from "deadline" to the newly created > > "mq-deadline" scheduler (bsc#1176574) > > (It takes us to 2.1.0-18.26.1 in case anyone's counting.) > > > > So two questions. First, it looks to me like mq-deadline is already there: > > $ rpm -q s390-tools > > s390-tools-2.1.0-18.23.1.s390x > > $ cat /sys/block/dasda/queue/scheduler > > [none] mq-deadline kyber bfq > > It's available, but what's currently in use is "none." That's the value > that's in square braces. > > > so what does the patch do? Second, how does the choice affect performance > > on DASD devices? Does one even have a choice or does the device driver > > allow only mq-deadline? > > It sets the scheduler to use mq-deadline (multi-queue deadline). You > could, if you choose, override that with one of the other choices, but I > wouldn't do that without getting some indication from one of IBM's > performance folks that you should. Our direction from that source was > that with the introduction of mq-deadline, that it was a better > _default_ than any of the others. >
Its also worth mentioning that "mq-deadline" is basically a straight forward port of the old "deadline", just that it uses the new block device request queue architecture (`blk-mq`, which dasd also implements in the kernel you have). So functionality wise it doesn't change anything; "deadline" and "mq-deadline" essentially have the same scheduling algorithm. IOW, in the past the DASD device driver implemented the older block device request queue architecture; for this older driver s390-tools would use "deadline" as default scheduler. Now the DASD device driver implements the new architecture; and for that s390-tools uses "mq-deadline" as default scheduler. Which, like I said above, is essentially the same scheduling algorithm. -- Best Regards, Benjamin Block / Linux on IBM Z Kernel Development / IBM Systems IBM Deutschland Research & Development GmbH / https://www.ibm.com/privacy Vorsitz. AufsR.: Gregor Pillen / Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen / Registergericht: AmtsG Stuttgart, HRB 243294 ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www2.marist.edu/htbin/wlvindex?LINUX-390
