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Hi,
I am doing some performance tuning in MR driver to understand how sdev queue
depth and hba queue depth play role in IO submission from above layer.
I have 24 JBOD connected to MR 12GB controller and I can see performance for 4K
Sequential work load as below.
HBA QD for MR controller is 4065 and Per device QD is set to 32
queue depth from <fio> 256 reports 300K IOPS
queue depth from <fio> 128 reports 330K IOPS
queue depth from <fio> 64 reports 360K IOPS
queue depth from <fio> 32 reports 510K IOPS
In MR driver I added debug print and confirm that more IO come to driver as
random IO whenever I have <fio> queue depth more than 32.
I have debug using scsi logging level and blktrace as well. Below is snippet of
logs using scsi logging level. In summary, if SML do flow control of IO due to
Device QD or HBA QD, IO coming to LLD is more random pattern.
I see IO coming to driver is not sequential.
[79546.912041] sd 18:2:21:0: [sdy] tag#854 CDB: Write(10) 2a 00 00 03 c0 3b 00
00 01 00
[79546.912049] sd 18:2:21:0: [sdy] tag#855 CDB: Write(10) 2a 00 00 03 c0 3c 00
00 01 00
[79546.912053] sd 18:2:21:0: [sdy] tag#886 CDB: Write(10) 2a 00 00 03 c0 5b 00
00 01 00
<KD> After LBA "00 03 c0 3c" next command is with LBA "00 03 c0 5b".
Two Sequence are overlapped due to sdev QD throttling.
[79546.912056] sd 18:2:21:0: [sdy] tag#887 CDB: Write(10) 2a 00 00 03 c0 5c 00
00 01 00
[79546.912250] sd 18:2:21:0: [sdy] tag#856 CDB: Write(10) 2a 00 00 03 c0 3d 00
00 01 00
[79546.912257] sd 18:2:21:0: [sdy] tag#888 CDB: Write(10) 2a 00 00 03 c0 5d 00
00 01 00
[79546.912259] sd 18:2:21:0: [sdy] tag#857 CDB: Write(10) 2a 00 00 03 c0 3e 00
00 01 00
[79546.912268] sd 18:2:21:0: [sdy] tag#858 CDB: Write(10) 2a 00 00 03 c0 3f 00
00 01 00
If scsi_request_fn() breaks due to unavailability of device queue (due to
below check), will there be any side defect as I observe ?
if (!scsi_dev_queue_ready(q, sdev))
break;
If I reduce HBA QD and make sure IO from above layer is throttled due to HBA
QD, there is a same impact.
MR driver use host wide shared tag map.
Can someone help me if this can be tunable in LLD providing additional settings
or it is expected behavior ? Problem I am facing is, I am not able to figure
out optimal device queue depth for different configuration and work load.
Thanks, Kashyap
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