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From: "Ewan D. Milne" <emilne@redhat.com>
To: Bart Van Assche <bvanassche@acm.org>,
	Ming Lei <ming.lei@redhat.com>, Hannes Reinecke <hare@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org,
	"James E . J . Bottomley" <jejb@linux.ibm.com>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	linux-scsi@vger.kernel.org,
	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>,
	Sumit Saxena <sumit.saxena@broadcom.com>,
	Shivasharan S <shivasharan.srikanteshwara@broadcom.com>,
	Christoph Hellwig <hch@lst.de>,
	Bart Van Assche <bart.vanassche@wdc.com>
Subject: Re: [PATCH 4/4] scsi: core: don't limit per-LUN queue depth for SSD
Date: Mon, 25 Nov 2019 13:28:49 -0500	[thread overview]
Message-ID: <e9cb5e75681537443b393ed1631857df81b8894d.camel@redhat.com> (raw)
In-Reply-To: <5f84476f-95b4-79b6-f72d-4e2de447065c@acm.org>

On Fri, 2019-11-22 at 10:14 -0800, Bart Van Assche wrote:
> 
> Hi Ming,
> 
> Thanks for having shared these numbers. I think this is very useful 
> information. Do these results show the performance drop that happens if 
> /sys/block/.../device/queue_depth exceeds .can_queue? What I am 
> wondering about is how important these results are in the context of 
> this discussion. Are there any modern SCSI devices for which a SCSI LLD 
> sets scsi_host->can_queue and scsi_host->cmd_per_lun such that the 
> device responds with BUSY? What surprised me is that only three SCSI 
> LLDs call scsi_track_queue_full() (mptsas, bfa, esp_scsi). Does that 
> mean that BUSY responses from a SCSI device or HBA are rare?
> 

Some FC HBAs end up returning busy from ->queuecommand() but I think
this is more commonly due to there being and issue with the rport rather
than the device.

-Ewan


  parent reply	other threads:[~2019-11-25 18:29 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-18 10:31 [PATCH 0/4] scis: don't apply per-LUN queue depth for SSD Ming Lei
2019-11-18 10:31 ` [PATCH 1/4] scsi: megaraid_sas: use private counter for tracking inflight per-LUN commands Ming Lei
2019-11-20  9:54   ` Hannes Reinecke
2019-11-26  3:12     ` Kashyap Desai
2019-11-26  3:37       ` Ming Lei
2019-12-05 10:32         ` Kashyap Desai
2019-11-18 10:31 ` [PATCH 2/4] scsi: mpt3sas: " Ming Lei
2019-11-20  9:55   ` Hannes Reinecke
2019-11-18 10:31 ` [PATCH 3/4] scsi: sd: register request queue after sd_revalidate_disk is done Ming Lei
2019-11-20  9:59   ` Hannes Reinecke
2019-11-18 10:31 ` [PATCH 4/4] scsi: core: don't limit per-LUN queue depth for SSD Ming Lei
2019-11-20 10:05   ` Hannes Reinecke
2019-11-20 17:00     ` Ewan D. Milne
2019-11-20 20:56       ` Bart Van Assche
2019-11-20 21:36         ` Ewan D. Milne
2019-11-22  2:25           ` Martin K. Petersen
2019-11-21  1:07         ` Ming Lei
2019-11-22  2:59           ` Martin K. Petersen
2019-11-22  3:24             ` Ming Lei
2019-11-22 16:38             ` Sumanesh Samanta
2019-11-21  0:08       ` Sumanesh Samanta
2019-11-21  0:54       ` Ming Lei
2019-11-21 19:19         ` Ewan D. Milne
2019-11-21  0:53     ` Ming Lei
2019-11-21 15:45       ` Hannes Reinecke
2019-11-22  8:09         ` Ming Lei
2019-11-22 18:14           ` Bart Van Assche
2019-11-22 18:26             ` James Smart
2019-11-22 20:46               ` Bart Van Assche
2019-11-22 22:04                 ` Ming Lei
2019-11-22 22:00             ` Ming Lei
2019-11-25 18:28             ` Ewan D. Milne [this message]
2019-11-25 22:14               ` James Smart
2019-11-22  2:18     ` Martin K. Petersen
2019-11-20 21:58 Sumanesh Samanta
2019-11-21  1:21 ` Ming Lei
2019-11-21  1:50   ` Sumanesh Samanta
2019-11-21  2:23     ` Ming Lei

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