* Question regarding output of btrace and use of blk-mq
@ 2021-11-18 2:17 Karan Tilak Kumar (kartilak)
2021-11-18 2:32 ` Jens Axboe
0 siblings, 1 reply; 2+ messages in thread
From: Karan Tilak Kumar (kartilak) @ 2021-11-18 2:17 UTC (permalink / raw)
To: linux-btrace
Hello btrace community,
I came across blktrace and blkparse tools as a part of my learning on blk-mq.
I'm trying to test some code in my driver and I want to test a few things by turning multiqueue on and off, and compare results.
I'm running IOs using medusa on my multipath device /dev/dm-2
When I turn off mq, I still see IOs queued from each CPU:
CPU0 (dm-2):
Reads Queued: 1,980, 199,438KiB Writes Queued: 1,344, 172,032KiB
Read Dispatches: 3,429, 199,894KiB Write Dispatches: 2,688, 172,032KiB
Reads Requeued: 0 Writes Requeued: 0
Reads Completed: 6,826, 199,130KiB Writes Completed: 5,376, 172,032KiB
Read Merges: 0, 0KiB Write Merges: 0, 0KiB
Read depth: 70 Write depth: 64
IO unplugs: 3,177 Timer unplugs: 0
CPU1 (dm-2):
Reads Queued: 2,101, 247,313KiB Writes Queued: 1,856, 237,568KiB
Read Dispatches: 3,986, 247,177KiB Write Dispatches: 3,709, 237,376KiB
Reads Requeued: 0 Writes Requeued: 0
Reads Completed: 7,975, 247,177KiB Writes Completed: 7,545, 241,344KiB
Read Merges: 0, 0KiB Write Merges: 0, 0KiB
Read depth: 70 Write depth: 64
IO unplugs: 3,899 Timer unplugs: 0
CPU2 (dm-2):
Reads Queued: 1,907, 224,925KiB Writes Queued: 1,760, 225,280KiB
Read Dispatches: 3,635, 224,793KiB Write Dispatches: 3,524, 225,536KiB
Reads Requeued: 0 Writes Requeued: 0
Reads Completed: 7,273, 224,793KiB Writes Completed: 7,044, 225,536KiB
Read Merges: 0, 0KiB Write Merges: 0, 0KiB
Read depth: 70 Write depth: 64
IO unplugs: 3,625 Timer unplugs: 1
CPU3 (dm-2):
Reads Queued: 1,572, 173,940KiB Writes Queued: 1,408, 180,224KiB
Read Dispatches: 2,885, 173,753KiB Write Dispatches: 2,815, 180,160KiB
Reads Requeued: 0 Writes Requeued: 0
Reads Completed: 5,766, 173,541KiB Writes Completed: 5,631, 180,160KiB
Read Merges: 0, 0KiB Write Merges: 0, 0KiB
Read depth: 70 Write depth: 64
IO unplugs: 2,922 Timer unplugs: 0
#cat /sys/module/scsi_mod/parameters/use_blk_mq
N
#cat /sys/module/dm_mod/parameters/use_blk_mq
N
When multiqueue is off, we don't expect IOs from all CPUs. Is this correct?
I've tried running medusa with one thread, and with eight threads on separate occasions, and I see IOs from all CPUs each time.
Is this expected? Please advise.
Thanks,
Karan
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Question regarding output of btrace and use of blk-mq
2021-11-18 2:17 Question regarding output of btrace and use of blk-mq Karan Tilak Kumar (kartilak)
@ 2021-11-18 2:32 ` Jens Axboe
0 siblings, 0 replies; 2+ messages in thread
From: Jens Axboe @ 2021-11-18 2:32 UTC (permalink / raw)
To: linux-btrace
On 11/17/21 7:17 PM, Karan Tilak Kumar (kartilak) wrote:
> Hello btrace community,
>
> I came across blktrace and blkparse tools as a part of my learning on blk-mq.
> I'm trying to test some code in my driver and I want to test a few things by turning multiqueue on and off, and compare results.
> I'm running IOs using medusa on my multipath device /dev/dm-2
>
> When I turn off mq, I still see IOs queued from each CPU:
>
> CPU0 (dm-2):
> Reads Queued: 1,980, 199,438KiB Writes Queued: 1,344, 172,032KiB
> Read Dispatches: 3,429, 199,894KiB Write Dispatches: 2,688, 172,032KiB
> Reads Requeued: 0 Writes Requeued: 0
> Reads Completed: 6,826, 199,130KiB Writes Completed: 5,376, 172,032KiB
> Read Merges: 0, 0KiB Write Merges: 0, 0KiB
> Read depth: 70 Write depth: 64
> IO unplugs: 3,177 Timer unplugs: 0
> CPU1 (dm-2):
> Reads Queued: 2,101, 247,313KiB Writes Queued: 1,856, 237,568KiB
> Read Dispatches: 3,986, 247,177KiB Write Dispatches: 3,709, 237,376KiB
> Reads Requeued: 0 Writes Requeued: 0
> Reads Completed: 7,975, 247,177KiB Writes Completed: 7,545, 241,344KiB
> Read Merges: 0, 0KiB Write Merges: 0, 0KiB
> Read depth: 70 Write depth: 64
> IO unplugs: 3,899 Timer unplugs: 0
> CPU2 (dm-2):
> Reads Queued: 1,907, 224,925KiB Writes Queued: 1,760, 225,280KiB
> Read Dispatches: 3,635, 224,793KiB Write Dispatches: 3,524, 225,536KiB
> Reads Requeued: 0 Writes Requeued: 0
> Reads Completed: 7,273, 224,793KiB Writes Completed: 7,044, 225,536KiB
> Read Merges: 0, 0KiB Write Merges: 0, 0KiB
> Read depth: 70 Write depth: 64
> IO unplugs: 3,625 Timer unplugs: 1
> CPU3 (dm-2):
> Reads Queued: 1,572, 173,940KiB Writes Queued: 1,408, 180,224KiB
> Read Dispatches: 2,885, 173,753KiB Write Dispatches: 2,815, 180,160KiB
> Reads Requeued: 0 Writes Requeued: 0
> Reads Completed: 5,766, 173,541KiB Writes Completed: 5,631, 180,160KiB
> Read Merges: 0, 0KiB Write Merges: 0, 0KiB
> Read depth: 70 Write depth: 64
> IO unplugs: 2,922 Timer unplugs: 0
>
>
> #cat /sys/module/scsi_mod/parameters/use_blk_mq
> N
> #cat /sys/module/dm_mod/parameters/use_blk_mq
> N
>
>
> When multiqueue is off, we don't expect IOs from all CPUs. Is this correct?
> I've tried running medusa with one thread, and with eight threads on separate occasions, and I see IOs from all CPUs each time.
> Is this expected? Please advise.
Yes this is expected, non blk-mq will still submit from any CPU that happens
to be issuing the IO.
--
Jens Axboe
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2021-11-18 2:32 ` Jens Axboe
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