On Tue, Feb 27 2007, Evgeniy Polyakov wrote: > On Tue, Feb 27, 2007 at 07:45:41PM +0100, Jens Axboe ([EMAIL PROTECTED]) > wrote: > > > Deadline shows this: > > > > > > sync: > > > READ: io=1,024MiB, aggrb=38,212KiB/s, minb=38,212KiB/s, > > > maxb=38,212KiB/s, mint=28099msec, maxt=28099msec > > > > > > libaio: > > > READ: io=1,024MiB, aggrb=37,933KiB/s, minb=37,933KiB/s, > > > maxb=37,933KiB/s, mint=28306msec, maxt=28306msec > > > > > > syslet-rw: > > > READ: io=1,024MiB, aggrb=34,759KiB/s, minb=34,759KiB/s, > > > maxb=34,759KiB/s, mint=30891msec, maxt=30891msec > > > > > > There were about 10k async schedulings. > > > > I think the issue here is pretty simple - when fio gets a queue full > > like condition (it reaches the depth you set, 32), it commits them and > > starts queuing again. Since that'll likely block, it'll get issued by > > another process. So you suddenly have a nice sequence of reads from one > > process (pending, only one is actually committed since it's serialized), > > and then a read further down the line that goes behind those you already > > committed. Then result is seeky, where it should have been sequential. > > > > Do you get expected results if you set iodepth_low=1? That'll make fio > > drain the queue before building it up again, should get you a sequential > > access pattern with syslets. > > With such a change results should be better - not only because seek is > removed with sequential read, but also number of working threads > decreases with time - until queue is filled again.
Yep, although it probably doesn't matter for such a low bandwidth test anyway. > So, syslet-rw has increased to 37mb/sec out of 39/sync and 38/libaio, > the latter two did not changed. I wonder why all three aren't doing 39mb/sec flat here, it's a pretty trivial case... > With iodepth of 10k, I get the same performance for > libaio and syslets - about 36mb/sec, it does not depend on iodepth_low > being set to 1 or default (full). Yep, the larger the iodepth, the less costly a seek on new queue buildup gets. So that is as expected. > So syslets have small problems with small number of iodepth - its > performance is about 34mb/sec and then increases to 36 with iodepth > grow. While libaio decreases from 38 down to 36 mb/sec. Using your job file and fio HEAD (forces iodepth_low=1 for syslet if iodepth_low isn't specified), I get: Engine Depth Bw (kb/sec) ----------------------------------- syslet 1 37163 syslet 32 37197 syslet 10000 36577 libaio 1 37144 libaio 32 37159 libaio 10000 36463 sync 1 37154 Results are highly stable. Note that this test case isn't totally fair, since libaio isn't really async when you do buffered file IO. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/