Vivek Goyal wrote: > On Tue, Jun 23, 2009 at 02:44:08PM +0800, Gui Jianfeng wrote: >> Vivek Goyal wrote: >>> On Mon, Jun 22, 2009 at 03:44:08PM +0800, Gui Jianfeng wrote: >>>> Preempt the ongoing non-rt ioq if there are rt ioqs waiting for dispatching >>>> in ancestor or sibling groups. It will give other group's rt ioq an chance >>>> to dispatch ASAP. >>>> >>> Hi Gui, >>> >>> Will new preempton logic of traversing up the hiearchy so that both new >>> queue and old queue are at same level to take a preemption decision not >>> take care of above scenario? >> Hi Vivek, >> >> Would you explain a bit what do you mean about "both new queue and old queue >> are at same level to take a preemption decision". I don't understand it well. >> > > Consider following hierarchy. > > root > / | > A 1 > | > 2 > In the above diagram, A is the group and "1" and "2" are two io queues > associated with tasks. > > Now assume that queue "1" is being served and queue "2" gets backlogged. > Should queue 2 preempt queue 1 now? > > To take that decision, we need to do the comparision between type of > entity of group A and queue 1 (That is at the same level or IOW, the > entities in question have the same parent). If group A is of class RT and > queue 1 is of type BE then queue 2 should preempt queue 1 otherwise not. > > Hence in hierarchical setups to take a preemption decision, comparison > should be done at same level. So what bfq_find_matching_entity has done is going to figure out the same level entities， in turn, taking the decision. > >>> Please have a look at bfq_find_matching_entity(). >>> >>> At the same time we probably don't want to preempt the non-rt queue >>> with an RT queue in sibling group until and unless sibling group is an >>> RT group. >>> >>> root >>> / \ >>> BEgrpA BEgrpB >>> | | >>> BEioq1 RTioq2 >>> >>> Above we got two BE group A and B and assume ioq in group A is being >>> served and then an RT request in group B comes. Because group B is an >>> BE class group, we should not preempt the queue in group A. >> Yes, i also have this concern. So, it does not allow non-rt group preempts >> another group. I'll check whether there is a way to address this issue. >> > > So here also assume ioq1 is being served and ioq2 gets backlogged. To > decide whether ioq2 should preempt ioq1 or not, one needs to go up the > hiearchy till two paths share the parent. That means one needs to go up > at the BEgrpA and BEgrpB level where they have common parent "root". Now > both the groups are of class BE hence ioq2 should not preempt ioq1. > > Hope it helps. Thanks, it's very helpful. I have a thought now. Whether we can maintain a rt ioq list in efqd, and elv_fq_select_ioq() travels this list to take preemtion decision for each available rt ioqs at the same level(by using bfq_find_matching_entity). I'd like to try it out. > > Thanks > Vivek > > > -- Regards Gui Jianfeng -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
