> Il giorno 27 giu 2017, alle ore 20:29, Jens Axboe <axboe@xxxxxxxxx> ha scritto: > > On 06/27/2017 12:27 PM, Paolo Valente wrote: >> >>> Il giorno 27 giu 2017, alle ore 16:41, Jens Axboe <axboe@xxxxxxxxx> ha scritto: >>> >>> On 06/27/2017 12:09 AM, Paolo Valente wrote: >>>> >>>>> Il giorno 19 giu 2017, alle ore 13:43, Paolo Valente <paolo.valente@xxxxxxxxxx> ha scritto: >>>>> >>>>> This commit fixes a bug triggered by a non-trivial sequence of >>>>> events. These events are briefly described in the next two >>>>> paragraphs. The impatiens, or those who are familiar with queue >>>>> merging and splitting, can jump directly to the last paragraph. >>>>> >>>>> On each I/O-request arrival for a shared bfq_queue, i.e., for a >>>>> bfq_queue that is the result of the merge of two or more bfq_queues, >>>>> BFQ checks whether the shared bfq_queue has become seeky (i.e., if too >>>>> many random I/O requests have arrived for the bfq_queue; if the device >>>>> is non rotational, then random requests must be also small for the >>>>> bfq_queue to be tagged as seeky). If the shared bfq_queue is actually >>>>> detected as seeky, then a split occurs: the bfq I/O context of the >>>>> process that has issued the request is redirected from the shared >>>>> bfq_queue to a new non-shared bfq_queue. As a degenerate case, if the >>>>> shared bfq_queue actually happens to be shared only by one process >>>>> (because of previous splits), then no new bfq_queue is created: the >>>>> state of the shared bfq_queue is just changed from shared to non >>>>> shared. >>>>> >>>>> Regardless of whether a brand new non-shared bfq_queue is created, or >>>>> the pre-existing shared bfq_queue is just turned into a non-shared >>>>> bfq_queue, several parameters of the non-shared bfq_queue are set >>>>> (restored) to the original values they had when the bfq_queue >>>>> associated with the bfq I/O context of the process (that has just >>>>> issued an I/O request) was merged with the shared bfq_queue. One of >>>>> these parameters is the weight-raising state. >>>>> >>>>> If, on the split of a shared bfq_queue, >>>>> 1) a pre-existing shared bfq_queue is turned into a non-shared >>>>> bfq_queue; >>>>> 2) the previously shared bfq_queue happens to be busy; >>>>> 3) the weight-raising state of the previously shared bfq_queue happens >>>>> to change; >>>>> the number of weight-raised busy queues changes. The field >>>>> wr_busy_queues must then be updated accordingly, but such an update >>>>> was missing. This commit adds the missing update. >>>>> >>>> >>>> Hi Jens, >>>> any idea of the possible fate of this fix? >>> >>> I sort of missed this one. It looks trivial enough for 4.12, or we >>> can defer until 4.13. What do you think? >>> >> >> It should actually be something trivial, and hopefully correct, >> because a further throughput improvement (for BFQ), which depends on >> this fix, is now working properly, and we didn't see any regression so >> far. In addition, since this improvement is virtually ready for >> submission, further steps may be probably easier if this fix gets in >> sooner (whatever the luck of the improvement will be). > > OK, let's queue it up for 4.13 then. > My arguments was in favor of 4.12 actually. Maybe you did mean 4.12 here? Thanks, Paolo > -- > Jens Axboe
