From: Jens Axboe <axboe@suse.de>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: James Bottomley <James.Bottomley@SteelEye.com>,
Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [BK PATCHES] add ata scsi driver
Date: Mon, 26 May 2003 22:38:00 +0200 [thread overview]
Message-ID: <20030526203800.GP845@suse.de> (raw)
In-Reply-To: <Pine.LNX.4.44.0305261317520.12186-100000@home.transmeta.com>
On Mon, May 26 2003, Linus Torvalds wrote:
>
> On 26 May 2003, James Bottomley wrote:
> >
> > On Mon, 2003-05-26 at 15:07, Jens Axboe wrote:
> > > Alright, so what do you need? Start out with X tags, shrink to Y (based
> > > on repeated queue full conditions)? Anything else?
> >
> > Actually, it's easier than that: just an API to alter the number of tags
> > in the block layer (really only the size of your internal hash table).
> > The actual heuristics of when to alter the queue depth is the province
> > of the individual drivers (although Doug Ledford was going to come up
> > with a generic implementation).
>
> Talking about tagged queueing - does the SCSI layer still remove the
> request from the request list when it starts executing it?
Yes
> At least historically that's a major mistake, and generates a crappy
> elevator, because it removes information from the block layer about where
> the disk is (or is going to be).
Not necessarily, the io schedulers keep track of where we are going. You
don't need an active front request for that.
> I know Andrew thinks that SCSI tagged queuing is a bunch of crap, and he
> has the latency numbers to prove it. He blames the SCSI disks themselves,
> but I think it might be the fact that SCSI makes it impossible to make a
> fair queuing algorithm for higher levels by hiding information.
>
> Has anybody looked at just removing the request at command _completion_
> time instead? That's what IDE does, and it's the _right_ thing to do.
I know this is a pet peeve of yours (must be, I remember you bringing it
up at least 3 time before :), but I don't think that's necessarily true.
It shouldn't matter _one_ bit whether you leave the request there or
not, it's unmergeable. As long as the io scheduler keeps track of this
(and it does!) we are golden.
--
Jens Axboe
next prev parent reply other threads:[~2003-05-26 20:24 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-26 18:12 [BK PATCHES] add ata scsi driver James Bottomley
2003-05-26 18:18 ` Jens Axboe
2003-05-26 18:47 ` James Bottomley
2003-05-26 19:07 ` Jens Axboe
2003-05-26 19:17 ` James Bottomley
2003-05-26 19:33 ` Jens Axboe
2003-05-27 12:39 ` Jens Axboe
2003-05-27 14:26 ` James Bottomley
2003-05-27 17:16 ` Jens Axboe
2003-05-27 18:09 ` James Bottomley
2003-05-27 18:21 ` Jens Axboe
2003-05-27 18:30 ` James Bottomley
2003-05-26 20:27 ` Linus Torvalds
2003-05-26 20:36 ` James Bottomley
2003-05-26 20:45 ` Linus Torvalds
2003-05-26 20:51 ` Jens Axboe
2003-05-26 20:56 ` James Bottomley
2003-05-26 20:38 ` Jens Axboe [this message]
2003-05-26 20:49 ` Linus Torvalds
2003-05-26 20:57 ` Jens Axboe
2003-05-26 21:34 ` Linus Torvalds
2003-05-26 23:58 ` Nick Piggin
2003-05-27 0:09 ` Linus Torvalds
2003-05-27 0:49 ` Nick Piggin
2003-05-27 0:16 ` Alan Cox
2003-05-27 6:54 ` Jens Axboe
2003-05-27 14:20 ` James Bottomley
2003-05-27 14:36 ` Linus Torvalds
2003-05-27 14:59 ` James Bottomley
2003-05-27 15:21 ` Jeff Garzik
2003-05-27 15:38 ` James Bottomley
2003-05-27 15:50 ` Jeff Garzik
2003-05-27 16:00 ` James Bottomley
2003-05-27 16:16 ` Jeff Garzik
2003-05-28 9:35 ` Christoph Hellwig
2003-05-28 10:50 ` Lincoln Dale
2003-05-27 19:43 ` Jens Axboe
-- strict thread matches above, loose matches on Subject: below --
2003-05-26 4:58 Jeff Garzik
2003-05-26 5:15 ` Linus Torvalds
2003-05-26 5:30 ` Jeff Garzik
2003-05-26 5:36 ` Jeff Garzik
2003-05-26 5:42 ` Linus Torvalds
2003-05-26 6:01 ` Jeff Garzik
2003-05-26 16:56 ` Linus Torvalds
2003-05-26 17:47 ` Jeff Garzik
2003-05-26 20:09 ` Linus Torvalds
2003-05-27 0:29 ` Alan Cox
2003-05-27 6:07 ` Jeff Garzik
2003-05-27 6:30 ` Linus Torvalds
2003-05-27 6:51 ` Linus Torvalds
2003-05-27 7:29 ` Jeff Garzik
2003-05-26 5:40 ` Linus Torvalds
2003-05-26 5:53 ` Jeff Garzik
2003-05-26 6:21 ` Jeff Garzik
2003-05-26 16:57 ` Linus Torvalds
2003-05-26 17:24 ` Jens Axboe
2003-05-26 17:54 ` Jeff Garzik
2003-05-26 17:59 ` Jeff Garzik
2003-05-26 18:11 ` Jens Axboe
2003-05-27 0:22 ` Alan Cox
2003-05-27 4:15 ` Linus Torvalds
2003-05-26 10:32 ` Bartlomiej Zolnierkiewicz
2003-05-26 11:13 ` Jeff Garzik
2003-05-26 11:37 ` Bartlomiej Zolnierkiewicz
2003-05-26 5:59 ` Benjamin Herrenschmidt
2003-05-26 6:03 ` Jeff Garzik
2003-06-02 9:46 ` Andre Hedrick
2003-06-02 13:56 ` Alan Cox
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