> Il giorno 11 giu 2020, alle ore 10:31, Jan Kara <jack@xxxxxxx> ha scritto: > > On Thu 11-06-20 09:13:07, Paolo Valente wrote: >> >> >>> Il giorno 5 giu 2020, alle ore 16:16, Jan Kara <jack@xxxxxxx> ha scritto: >>> >>> bfq_setup_cooperator() uses bfqd->in_serv_last_pos so detect whether it >>> makes sense to merge current bfq queue with the in-service queue. >>> However if the in-service queue is freshly scheduled and didn't dispatch >>> any requests yet, bfqd->in_serv_last_pos is stale and contains value >>> from the previously scheduled bfq queue which can thus result in a bogus >>> decision that the two queues should be merged. >> >> Good catch! >> >>> This bug can be observed >>> for example with the following fio jobfile: >>> >>> [global] >>> direct=0 >>> ioengine=sync >>> invalidate=1 >>> size=1g >>> rw=read >>> >>> [reader] >>> numjobs=4 >>> directory=/mnt >>> >>> where the 4 processes will end up in the one shared bfq queue although >>> they do IO to physically very distant files (for some reason I was able to >>> observe this only with slice_idle=1ms setting). >>> >>> Fix the problem by invalidating bfqd->in_serv_last_pos when switching >>> in-service queue. >>> >> >> Apart from the nonexistent problem that even 0 is a valid LBA :) > > Yes, I was also thinking about that and decided 0 is "good enough" :). But > I just as well just switch to (sector_t)-1 if you think it would be better. > 0 is ok :) Thanks, Paolo >> Acked-by: Paolo Valente <paolo.valente@xxxxxxxxxx> > > Thanks! > > Honza > > -- > Jan Kara <jack@xxxxxxxx> > SUSE Labs, CR
