From: Doug Ledford <dledford@redhat.com>
To: "Justin T. Gibbs" <gibbs@scsiguy.com>
Cc: James Bottomley <James.Bottomley@steeleye.com>,
Andrew Morton <akpm@digeo.com>, Jens Axboe <axboe@suse.de>,
Matthew Jacob <mjacob@feral.com>,
"Pedro M. Rodrigues" <pmanuel@myrealbox.com>,
Mathieu Chouquet-Stringer <mathieu@newview.com>,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Warning - running *really* short on DMA buffers while doingfiletransfers
Date: Mon, 30 Sep 2002 19:54:13 -0400 [thread overview]
Message-ID: <20020930235413.GH25340@redhat.com> (raw)
In-Reply-To: <2645346224.1033162127@aslan.btc.adaptec.com>
On Fri, Sep 27, 2002 at 03:28:47PM -0600, Justin T. Gibbs wrote:
> > Linux is perfectly happy just to have you return 1 in queuecommand if the
> > device won't accept the tag. The can_queue parameter represents the
> > maximum number of outstanding commands the mid-layer will ever send.
> > The mid-layer is happy to re-queue I/O below this limit if it cannot be
> > accepted by the drive. In fact, that's more or less what queue plugging
> > is about.
> >
> > The only problem occurs if you return 1 from queuecommand with no other
> > outstanding I/O for the device.
> >
> > There should be no reason in 2.5 for a driver to have to implement an
> > internal queue.
>
> Did this really get fixed in 2.5? The internal queuing was completely
> broken in 2.4. Some of the known breakages were:
>
> 1) Device returns queue full with no outstanding commands from us
> (usually occurs in multi-initiator environments).
This may be fixed.
> 2) No delay after busy status so devices that will continually
> report BUSY if you hammer them with commands never come ready.
This is still broken. Plus, it has a limited number of retries before it
simply returns an I/O error, so it basically hammers the device (so it
can't get unbusy) until a set number of retries have completed then it
returns an I/O error, giving all sorts of false I/O errors on devices that
use BUSY status.
> 3) Queue is restarted as soon as any command completes even if
> you really need to throttle down the number of tags supported
> by the device.
>
> 4) No tag throttling. If tag throttling is in 2.5, does it ever
> increment the tag depth to handle devices that report temporary
> resource shortages (Atlas II and III do this all the time, other
> devices usually do this only in multi-initiator environments).
The current 2.5 mid layer is still tag stupid. It has no concept of tag
depth adjustment (although I have a patch here that implements this bit,
it really needs updating to the current kernels).
> 5) Proper transaction ordering across a queue full. The aic7xxx
> driver "requeues" all transactions that have not yet been sent
> to the device replacing the transaction that experienced the queue
> full back at the head so that ordering is maintained.
>
> No thought was put into any of these issues in 2.4, so I decided not
> to even think about trusting the mid-layer for this functionality.
No, you still can't yet, but we hope to have that fixed before the next
stable kernel series.
--
Doug Ledford <dledford@redhat.com> 919-754-3700 x44233
Red Hat, Inc.
1801 Varsity Dr.
Raleigh, NC 27606
next prev parent reply other threads:[~2002-09-30 23:48 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-09-26 3:27 Warning - running *really* short on DMA buffers while doing file transfers Mathieu Chouquet-Stringer
2002-09-26 6:14 ` Jens Axboe
2002-09-26 7:04 ` Pedro M. Rodrigues
2002-09-26 15:31 ` Justin T. Gibbs
2002-09-27 6:13 ` Jens Axboe
2002-09-27 6:33 ` Matthew Jacob
2002-09-27 6:36 ` Jens Axboe
2002-09-27 6:50 ` Matthew Jacob
2002-09-27 6:56 ` Jens Axboe
2002-09-27 7:18 ` Matthew Jacob
2002-09-27 7:24 ` Jens Axboe
2002-09-27 7:29 ` Matthew Jacob
2002-09-27 7:34 ` Matthew Jacob
2002-09-27 7:45 ` Jens Axboe
2002-09-27 8:37 ` Matthew Jacob
2002-09-27 10:25 ` Jens Axboe
2002-09-27 12:18 ` Matthew Jacob
2002-09-27 12:54 ` Jens Axboe
2002-09-27 13:30 ` Justin T. Gibbs
2002-09-27 14:26 ` James Bottomley
2002-09-27 14:33 ` Jens Axboe
2002-09-27 16:26 ` Justin T. Gibbs
2002-09-27 17:21 ` James Bottomley
2002-09-27 18:56 ` Justin T. Gibbs
2002-09-27 19:07 ` Warning - running *really* short on DMA buffers while doingfile transfers Andrew Morton
2002-09-27 19:16 ` Justin T. Gibbs
2002-09-27 19:36 ` Warning - running *really* short on DMA buffers while doingfiletransfers Andrew Morton
2002-09-27 19:52 ` Justin T. Gibbs
2002-09-27 21:13 ` James Bottomley
2002-09-27 21:18 ` Matthew Jacob
2002-09-27 21:23 ` James Bottomley
2002-09-27 21:29 ` Justin T. Gibbs
2002-09-27 21:32 ` Matthew Jacob
2002-09-27 22:08 ` Mike Anderson
2002-09-30 23:49 ` Doug Ledford
2002-09-27 21:28 ` Justin T. Gibbs
2002-09-28 15:52 ` James Bottomley
2002-09-28 23:25 ` Luben Tuikov
2002-09-29 2:48 ` James Bottomley
2002-09-30 8:34 ` Jens Axboe
2002-09-29 4:00 ` Justin T. Gibbs
2002-09-29 15:45 ` James Bottomley
2002-09-29 16:49 ` [ getting OT ] " Matthew Jacob
2002-09-30 19:06 ` Luben Tuikov
2002-09-30 23:54 ` Doug Ledford [this message]
2002-09-27 19:58 ` Andrew Morton
2002-09-27 20:58 ` Warning - running *really* short on DMA buffers while doing file transfers Justin T. Gibbs
2002-09-27 21:38 ` Patrick Mansfield
2002-09-27 22:08 ` Justin T. Gibbs
2002-09-27 22:28 ` Patrick Mansfield
2002-09-27 22:48 ` Justin T. Gibbs
2002-09-27 18:59 ` Warning - running *really* short on DMA buffers while doingfile transfers Andrew Morton
2002-09-27 14:30 ` Warning - running *really* short on DMA buffers while doing file transfers Jens Axboe
2002-09-27 17:19 ` Justin T. Gibbs
2002-09-27 18:29 ` Rik van Riel
2002-09-27 14:56 ` Rik van Riel
2002-09-27 15:34 ` Matthew Jacob
2002-09-27 15:37 ` Jens Axboe
2002-09-27 17:20 ` Justin T. Gibbs
2002-09-27 12:28 ` Pedro M. Rodrigues
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