Hi, On 19 July 2017 at 18:22, Danny Al-Gaaf <danny.al-gaaf@xxxxxxxxx> wrote: > > I'm running into an issue with performance measurements on an iSCSI > volume. The volume has set a QoS value of max. 30.000 iops. > > I run tests with the libaio engine against the volume with the following > base parameter: > > fio --filename=/dev/sde --ioengine=libaio --direct=1 --buffered=0 > --atomic=1 --bs=4k --invalidate=0 > --readwrite=[read,write,randwrite,randread] --iodepth=128 --time_based > --runtime=1200 --name=ft --write_iops_log=w_iops_log > --write_bw_log=w_bw_log --write_lat_log=w_lat_log --output=fio_log > > With randread/randwrite everything is as expected. The volume reaches > the QoS max value and not more. But with write/read/readwrite I can get > over the max QoS IOPs: ~41k iops. > > After some investigation with wireshark it seems with seq r/w packages > are aggregated (e.g. 8k TCP packages instead of 4k), which they are not > with randwrite. > > Is there an issue in libaio or in fio? Or is it an expected behavior > from the kernel? Is fio's output (see "And finally, the disk statistics are printed" in http://fio.readthedocs.io/en/latest/fio_doc.html#interpreting-the-output ) saying that merges took place? If so if you tell the kernel to disable all merging (see nomerges in https://www.kernel.org/doc/Documentation/block/queue-sysfs.txt which talks about how it is possible to disable merging by writing 2 to the block device's nomerges parameter) does that change things? If so then I'd say you are seeing expected kernel behaviour. -- Sitsofe | http://sucs.org/~sits/ -- 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
