From: Hannes Reinecke <hare@suse.de>
To: "Martin K. Petersen" <martin.petersen@oracle.com>,
Tim Walker <tim.t.walker@seagate.com>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
Damien Le Moal <Damien.LeMoal@wdc.com>,
"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
linux-scsi <linux-scsi@vger.kernel.org>,
Ming Lei <ming.lei@redhat.com>
Subject: Re: [LSF/MM/BPF TOPIC] NVMe HDD
Date: Fri, 14 Feb 2020 08:32:57 +0100 [thread overview]
Message-ID: <2d66bb0b-29ca-6888-79ce-9e3518ee4b61@suse.de> (raw)
In-Reply-To: <yq1r1yzqfyb.fsf@oracle.com>
On 2/13/20 5:17 AM, Martin K. Petersen wrote:
>
> Tim,
>
>> SAS currently supports QD256, but the general consensus is that most
>> customers don't run anywhere near that deep. Does it help the system
>> for the HD to report a limited (256) max queue depth, or is it really
>> up to the system to decide many commands to queue?
>
> People often artificially lower the queue depth to avoid timeouts. The
> default timeout is 30 seconds from an I/O is queued. However, many
> enterprise applications set the timeout to 3-5 seconds. Which means that
> with deep queues you'll quickly start seeing timeouts if a drive
> temporarily is having issues keeping up (media errors, excessive spare
> track seeks, etc.).
>
> Well-behaved devices will return QF/TSF if they have transient resource
> starvation or exceed internal QoS limits. QF will cause the SCSI stack
> to reduce the number of I/Os in flight. This allows the drive to recover
> from its congested state and reduces the potential of application and
> filesystem timeouts.
>
This may even be a chance to revisit QoS / queue busy handling.
NVMe has this SQ head pointer mechanism which was supposed to handle
this kind of situations, but to my knowledge no-one has been
implementing it.
Might be worthwhile revisiting it; guess NVMe HDDs would profit from that.
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
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next prev parent reply other threads:[~2020-02-14 7:33 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-10 19:20 [LSF/MM/BPF TOPIC] NVMe HDD Tim Walker
2020-02-10 20:43 ` Keith Busch
2020-02-10 22:25 ` Finn Thain
2020-02-11 12:28 ` Ming Lei
2020-02-11 19:01 ` Tim Walker
2020-02-12 1:47 ` Damien Le Moal
2020-02-12 22:03 ` Ming Lei
2020-02-13 2:40 ` Damien Le Moal
2020-02-13 7:53 ` Ming Lei
2020-02-13 8:24 ` Damien Le Moal
2020-02-13 8:34 ` Ming Lei
2020-02-13 16:30 ` Keith Busch
2020-02-14 0:40 ` Ming Lei
2020-02-13 3:02 ` Martin K. Petersen
2020-02-13 3:12 ` Tim Walker
2020-02-13 4:17 ` Martin K. Petersen
2020-02-14 7:32 ` Hannes Reinecke [this message]
2020-02-14 14:40 ` Keith Busch
2020-02-14 16:04 ` Hannes Reinecke
2020-02-14 17:05 ` Keith Busch
2020-02-18 15:54 ` Tim Walker
2020-02-18 17:41 ` Keith Busch
2020-02-18 17:52 ` James Smart
2020-02-19 1:31 ` Ming Lei
2020-02-19 1:53 ` Damien Le Moal
2020-02-19 2:15 ` Ming Lei
2020-02-19 2:32 ` Damien Le Moal
2020-02-19 2:56 ` Tim Walker
2020-02-19 16:28 ` Tim Walker
2020-02-19 20:50 ` Keith Busch
2020-02-14 0:35 ` Ming Lei
2020-02-12 21:52 ` Ming Lei
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