On 01/18/2017 06:02 AM, Hannes Reinecke wrote: > On 01/17/2017 05:50 PM, Sagi Grimberg wrote: >> >>> So it looks like we are super not efficient because most of the >>> times we catch 1 >>> completion per interrupt and the whole point is that we need to find >>> more! This fio >>> is single threaded with QD=32 so I'd expect that we be somewhere in >>> 8-31 almost all >>> the time... I also tried QD=1024, histogram is still the same. >>> >>> >>> It looks like it takes you longer to submit an I/O than to service an >>> interrupt, >> >> Well, with irq-poll we do practically nothing in the interrupt handler, >> only schedule irq-poll. Note that the latency measures are only from >> the point the interrupt arrives and the point we actually service it >> by polling for completions. >> >>> so increasing queue depth in the singe-threaded case doesn't >>> make much difference. You might want to try multiple threads per core >>> with QD, say, 32 >> >> This is how I ran, QD=32. > > The one thing which I found _really_ curious is this: > > IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >> =64=100.0% > submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> =64=0.0% > complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> =64=0.1% > issued : total=r=7673377/w=0/d=0, short=r=0/w=0/d=0, > drop=r=0/w=0/d=0 > latency : target=0, window=0, percentile=100.00%, depth=256 > > (note the lines starting with 'submit' and 'complete'). > They are _always_ 4, irrespective of the hardware and/or tests which I > run. Jens, what are these numbers supposed to mean? > Is this intended? It's bucketized. 0=0.0% means that 0% of the submissions didn't submit anything (unsurprisingly), and ditto for the complete side. The next bucket is 1..4, so 100% of submissions and completions was in that range. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
