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. -- 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
