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From: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
To: "Martin K. Petersen" <martin.petersen@oracle.com>,
	linux-scsi@vger.kernel.org
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>,
	Jens Axboe <axboe@kernel.dk>,
	Sathya Prakash <sathya.prakash@broadcom.com>,
	Chaitra P B <chaitra.basappa@broadcom.com>,
	Suganath Prabu Subramani  <suganath-prabu.subramani@broadcom.com>,
	Kashyap Desai <kashyap.desai@broadcom.com>,
	Shivasharan S <shivasharan.srikanteshwara@broadcom.com>,
	"Ewan D . Milne" <emilne@redhat.com>,
	Christoph Hellwig <hch@lst.de>, Hannes Reinecke <hare@suse.de>,
	Bart Van Assche <bart.vanassche@wdc.com>,
	Ming Lei <ming.lei@redhat.com>,
	linux-block@vger.kernel.org,
	Sumit Saxena <sumit.saxena@broadcom.com>
Subject: RE: [PATCH 5/6] scsi: core: don't limit per-LUN queue depth for SSD when HBA needs
Date: Fri, 24 Jan 2020 12:41:20 -0700	[thread overview]
Message-ID: <f4f06cf8459c21749335c6b7a4cfe729@mail.gmail.com> (raw)
In-Reply-To: <yq1iml1ehtl.fsf@oracle.com>

Hi Martin,

>> Please read what I proposed. megaraid VDs don't report QUEUE_FULL so
you would not trigger the device_busy counter.

Yes, megaraid does not use set track_queue_depth, and never reports
QUEUE_FULL . Instead of relying on QUEUE_FULL and some complex heuristics
of when to start tracking device_busy, why can't we simply use  "
track_queue_depth" ( along with the other flag that Ming added) to decide
which devices need queue depth tracking, and track device_busy only for
them?

>>Something like not maintaining device_busy until we actually get a
>>QUEUE_FULL condition. And then rely on the existing queue depth ramp up
>>heuristics to determine when to disable the busy counter again.

I am not sure how we can suddenly start tracking device_busy on the fly,
if we do not know how many IO are already pending for that device? Won't
device_busy have a high chance of getting negative ( or at least wrong
value) when pending IOs start getting completed?

Thanks,
Sumanesh


-----Original Message-----
From: Martin K. Petersen <martin.petersen@oracle.com>
Sent: Thursday, January 23, 2020 6:59 PM
To: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Cc: linux-scsi@vger.kernel.org; Martin K. Petersen
<martin.petersen@oracle.com>
Subject: Re: [PATCH 5/6] scsi: core: don't limit per-LUN queue depth for
SSD when HBA needs


Sumanesh,

> The high-end controllers might expose a SCSI interface, but can have
> all kind of devices (NVMe/SCSI/SATA) behind it, and has its own
> capability to queue IO and feed to devices as needed. Those devices
> should not be penalized with the overhead of the device_busy counter,
> just because they chose to expose themselves has SCSI devices (for
> historical and backward compatibility reasons).

Please read what I proposed. megaraid VDs don't report QUEUE_FULL so you
would not trigger the device_busy counter.

-- 
Martin K. Petersen	Oracle Linux Engineering

  parent reply	other threads:[~2020-01-24 19:41 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-19  7:14 [PATCH 0/6] scsi: support bypass device busy check for some high end HBA with SSD Ming Lei
2020-01-19  7:14 ` [PATCH 1/6] scsi: mpt3sas: don't use .device_busy in device reset routine Ming Lei
2020-01-19 20:28   ` Bart Van Assche
2020-01-19  7:14 ` [PATCH 2/6] scsi: remove .for_blk_mq Ming Lei
2020-01-19 20:29   ` Bart Van Assche
2020-01-20 10:17   ` John Garry
2020-01-20 22:12   ` Elliott, Robert (Servers)
2020-01-31  6:30   ` Christoph Hellwig
2020-02-05  2:13     ` Martin K. Petersen
2020-01-19  7:14 ` [PATCH 3/6] scsi: sd: register request queue after sd_revalidate_disk is done Ming Lei
2020-01-19 20:36   ` Bart Van Assche
2020-01-19  7:14 ` [PATCH 4/6] block: freeze queue for updating QUEUE_FLAG_NONROT Ming Lei
2020-01-19 20:40   ` Bart Van Assche
2020-01-19  7:14 ` [PATCH 5/6] scsi: core: don't limit per-LUN queue depth for SSD when HBA needs Ming Lei
2020-01-19 20:58   ` Bart Van Assche
2020-01-21  4:52   ` Martin K. Petersen
2020-01-23  2:54     ` Ming Lei
2020-01-24  1:21       ` Martin K. Petersen
2020-01-24  1:59         ` Ming Lei
2020-01-24 12:43           ` Sumit Saxena
2020-01-28  4:04             ` Martin K. Petersen
     [not found]     ` <ab676c4c-03fb-7eb9-6212-129eb83d0ee8@broadcom.com>
     [not found]       ` <yq1iml1ehtl.fsf@oracle.com>
2020-01-24 19:41         ` Sumanesh Samanta [this message]
2020-01-28  4:22           ` Martin K. Petersen
2020-01-31 11:39             ` Ming Lei
2020-01-19  7:14 ` [PATCH 6/6] scsi: megaraid: set flag of no_device_queue_for_ssd Ming Lei

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