From: Jens Axboe <axboe@suse.de>
To: Luben Tuikov <luben@splentec.com>
Cc: James Bottomley <James.Bottomley@SteelEye.com>,
"Justin T. Gibbs" <gibbs@scsiguy.com>,
Andrew Morton <akpm@digeo.com>, 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 10:34:09 +0200 [thread overview]
Message-ID: <20020930083409.GI27420@suse.de> (raw)
In-Reply-To: <3D963A73.F593F5F7@splentec.com>
On Sat, Sep 28 2002, Luben Tuikov wrote:
> James Bottomley wrote:
> >
> > > 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.
> >
> > I'm lost here. We currently implement TCQ with simple tags which have no
> > guarantee of execution order in the drive I/O scheduler. Why would we want to
> > bother preserving the order of what will become essentially an unordered queue?
> >
> > This will become an issue when (or more likely if) journalled fs rely on the
> > barrier being implemented down to the medium, and the mid layer does do
> > reqeueing in the correct order in that case, except for the tiny race where
> > the command following the queue full could be accepted by the device before
> > the queue is blocked.
>
> Justin has the right idea.
>
> TCQ goes hand in hand with Task Attributes. I.e. a tagged task
> is an I_T_L_Q nexus and has a task attribute (Simple, Ordered, Head
> of Queue, ACA; cf. SAM-3, 4.9.1).
>
> Maybe the generator of tags (block layer, user process through sg, etc)
> should also set the tag attribute of the task, as per SAM-3.
> Most often (as currently implicitly) this would be a Simple task attribute.
> Why not the block layer borrow the idea from SAM-3, I see IDE only
> coming closer to SCSI...
Block layer being the tag generator (and manager), yes I 100% agree that
if we extend the support of block level tagging slightly it is very
possible to simply generate the type of tag required (as already replied
to Patrick, REQ_BARRIER would be an ordered task attribut, etc).
Currently IDE tcq has no notion of tag options, unfortunately.
> This way there'd be no need for explicit barriers. They can be implemented
> through Ordered and Head of Queue Tasks, everything else is Simple
> attribute task (IO scheduler can play with those as it wishes).
>
> This would provide for a more general basis the whole game (IO scheduling,
> TCQ, IO barriers, etc).
Agree
--
Jens Axboe
next prev parent reply other threads:[~2002-09-30 8:29 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 [this message]
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
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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