> Il giorno 16 gen 2023, alle ore 14:03, Jan Kara <jack@xxxxxxx> ha scritto: > > Hi Paolo! > > On Tue 03-01-23 15:54:55, Paolo Valente wrote: >> Here is the whole description of this patch series again. This >> extension addresses the following issue. Single-LUN multi-actuator >> SCSI drives, as well as all multi-actuator SATA drives appear as a >> single device to the I/O subsystem [1]. Yet they address commands to >> different actuators internally, as a function of Logical Block >> Addressing (LBAs). A given sector is reachable by only one of the >> actuators. For example, Seagate’s Serial Advanced Technology >> Attachment (SATA) version contains two actuators and maps the lower >> half of the SATA LBA space to the lower actuator and the upper half to >> the upper actuator. >> >> Evidently, to fully utilize actuators, no actuator must be left idle >> or underutilized while there is pending I/O for it. To reach this >> goal, the block layer must somehow control the load of each actuator >> individually. This series enriches BFQ with such a per-actuator >> control, as a first step. Then it also adds a simple mechanism for >> guaranteeing that actuators with pending I/O are never left idle. >> >> See [1] for a more detailed overview of the problem and of the >> solutions implemented in this patch series. There you will also find >> some preliminary performance results. > > Sorry, I didn't find time to look into this earlier. I've just had a > high-level look into the patches and I have one question: Did you consider > a solution where you'd basically duplicate all of the scheduling for each > actuator (thus making them effectively independent devices from the point > of view of BFQ)? Yep, I did. > From the first look it would look like somewhat simpler > solution than splitting all the BFQ queues and implementing special > injection mechanism for other actuators and perhaps lead to better > utilization of the actuators. OTOH the latecy and QoS for tasks using > multiple actuators would be probably worse because it would be basically > determined by the busiest of the actuators. Exactly, that's why I had to keep all queues in the same bucket. Thanks for both asking and answering! :) Jokes apart, thank you a lot for having a look at this contribution, Paolo > So I'm asking mostly out of > curiosity :) > > Honza > > -- > Jan Kara <jack@xxxxxxxx> > SUSE Labs, CR
