Messages in this thread |  | | | From | Aaron Carroll <> | | Date | Thu, 17 Apr 2008 20:19:13 +1000 | | Subject | Re: [RESEND][RFC] BFQ I/O Scheduler |
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Jens Axboe wrote: >> Maybe there is also another middle-ground solution. I'll try to sketch >> it out: >> . use sectors instead of time >> . impose a penalty to each thread in proportion to the distance between >> its disk requests >> . reduce the maximum budget of each thread as a function of this seek >> penalty so as to prevent the thread from stealing more than a given time >> slice (the simple mechanism to limit per-thread budget is already >> implemented in bfq). >> >> By doing so, both fairness and time isolation should be guaranteed. >> Finally, this policy should be safe in that, given the maximum time used >> by a seeky thread to consume its maximum budget on a reference disk, the >> time used on any faster disk should be shorter. >> >> Does it seem reasonable? > > Not for CFQ, that will stay time based. The problem with #2 above is > that it then quickly turns to various heuristics, which is just > impossible to tune for general behaviour. Or it just falls apart for > other real life situations.
Like SSD or hardware RAID. Time-slices have the nice property of fairness irrespective of the underlying hardware characteristics.
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