From: Jens Axboe <axboe@kernel.dk>
To: linux-btrace@vger.kernel.org
Subject: Re: Question regarding output of btrace and use of blk-mq
Date: Thu, 18 Nov 2021 02:32:53 +0000 [thread overview]
Message-ID: <59446380-a449-aada-61ab-d791f4839660@kernel.dk> (raw)
In-Reply-To: <SJ0PR11MB58966D3BE29649A350F098AEC39B9@SJ0PR11MB5896.namprd11.prod.outlook.com>
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
prev parent reply other threads:[~2021-11-18 2:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
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 [this message]
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