> Il giorno 31 mag 2018, alle ore 16:38, Jens Axboe <axboe@xxxxxxxxx> ha scritto: > > On 5/31/18 2:55 AM, Paolo Valente wrote: >> >> >>> Il giorno 27 mag 2018, alle ore 16:24, Sitsofe Wheeler <sitsofe@xxxxxxxxx> ha scritto: >>> >>> Hi Paolo! >>> >>> On 25 May 2018 at 20:20, Paolo Valente <paolo.valente@xxxxxxxxxx> wrote: >>>> Hi, >>>> if I run this job (even with the last version GitHub version of fio) on an SSD: >>>> [global] >>>> ioengine=sync >>>> time_based=1 >>>> runtime=20 >>>> readwrite=randread >>>> size=100m >>>> numjobs=1 >>>> invalidate=1 >>>> [job1] >>>> >>>> then, after little time (I think after 100MB have been read), fio reports a nonsensically large value for the throughput, while a simple iostat shows that no I/O is going on. By just replacing time_based with loops, i.e., with a job file like this: >>>> >>>> [global] >>>> ioengine=sync >>>> loops=1000 >>>> readwrite=randread >>>> size=100m >>>> numjobs=1 >>>> invalidate=1 >>>> [job1] >>>> >>>> the problem disappears. >>> >>> I've taken a stab at fixing this over in >>> https://github.com/sitsofe/fio/tree/random_reinvalidate - does that >>> solve the issue for you too? >> >> Nope :( >> >>> ... >>> I know I'm "Teaching grandmother to suck eggs" given that you're the >>> author of BFQ but just in case... >>> >>> This issue happens on loops=1000 too and I believe it's down to >>> readahead. >> >> I'm afraid there is a misunderstanding on this, grandson :) >> >> As I wrote, this problem does not occur with loops=1000. My >> impression is that, with loops, as well as with time-based and read, >> fio does invalidate the cache every time it restarts reading the same >> file, while with time_based and randread it does not (or maybe it >> tries to, but fails for some reason). > > This is basically by design. loop will go through the full > open+invalidate, whereas time_based will just keep chugging > along. Once your 100mb is in page cache, then no more IO > will be done, as reads are just served from there. > Such a design confused me. Highlighting somewhere this deviation (between loops and time_based) might help other dull people like me. Thanks, Paolo > -- > Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
