From: Keith Busch <kbusch@kernel.org>
To: Hannes Reinecke <hare@suse.de>
Cc: Damien Le Moal <Damien.LeMoal@wdc.com>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
linux-scsi <linux-scsi@vger.kernel.org>,
Tim Walker <tim.t.walker@seagate.com>,
"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
Ming Lei <ming.lei@redhat.com>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: [LSF/MM/BPF TOPIC] NVMe HDD
Date: Sat, 15 Feb 2020 02:05:14 +0900 [thread overview]
Message-ID: <20200214170514.GA10757@redsun51.ssa.fujisawa.hgst.com> (raw)
In-Reply-To: <d043a58d-6584-1792-4433-ac2cc39526ca@suse.de>
On Fri, Feb 14, 2020 at 05:04:25PM +0100, Hannes Reinecke wrote:
> On 2/14/20 3:40 PM, Keith Busch wrote:
> > On Fri, Feb 14, 2020 at 08:32:57AM +0100, Hannes Reinecke wrote:
> > > On 2/13/20 5:17 AM, Martin K. Petersen wrote:
> > > > 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.
> >
> > We don't need that because we don't allocate enough tags to potentially
> > wrap the tail past the head. If you can allocate a tag, the queue is not
> > full. And convesely, no tag == queue full.
> >
> It's not a problem on our side.
> It's a problem on the target/controller side.
> The target/controller might have a need to throttle I/O (due to QoS settings
> or competing resources from other hosts), but currently no means of
> signalling that to the host.
> Which, incidentally, is the underlying reason for the DNR handling
> discussion we had; NetApp tried to model QoS by sending "Namespace not
> ready" without the DNR bit set, which of course is a totally different
> use-case as the typical 'Namespace not ready' response we get (with the DNR
> bit set) when a namespace was unmapped.
>
> And that is where SQ head pointer updates comes in; it would allow the
> controller to signal back to the host that it should hold off sending I/O
> for a bit.
> So this could / might be used for NVMe HDDs, too, which also might have a
> need to signal back to the host that I/Os should be throttled...
Okay, I see. I think this needs a new nvme AER notice as Martin
suggested. The desired host behavior is simiilar to what we do with a
"firmware activation notice" where we temporarily quiesce new requests
and reset IO timeouts for previously dispatched requests. Perhaps tie
this to the CSTS.PP register as well.
_______________________________________________
linux-nvme mailing list
linux-nvme@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-nvme
next prev parent reply other threads:[~2020-02-14 17:05 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
2020-02-14 14:40 ` Keith Busch
2020-02-14 16:04 ` Hannes Reinecke
2020-02-14 17:05 ` Keith Busch [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200214170514.GA10757@redsun51.ssa.fujisawa.hgst.com \
--to=kbusch@kernel.org \
--cc=Damien.LeMoal@wdc.com \
--cc=hare@suse.de \
--cc=linux-block@vger.kernel.org \
--cc=linux-nvme@lists.infradead.org \
--cc=linux-scsi@vger.kernel.org \
--cc=martin.petersen@oracle.com \
--cc=ming.lei@redhat.com \
--cc=tim.t.walker@seagate.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).