From: "Stephen C. Tweedie" <sct@redhat.com>
To: Christoph Hellwig <hch@caldera.de>
Cc: "Stephen C. Tweedie" <sct@redhat.com>,
bsuparna@in.ibm.com, linux-kernel@vger.kernel.org,
kiobuf-io-devel@lists.sourceforge.net
Subject: Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait /notify + callback chains
Date: Thu, 1 Feb 2001 21:25:08 +0000 [thread overview]
Message-ID: <20010201212508.G11607@redhat.com> (raw)
In-Reply-To: <20010201193221.D11607@redhat.com> <200102012046.VAA16746@ns.caldera.de>
In-Reply-To: <200102012046.VAA16746@ns.caldera.de>; from hch@caldera.de on Thu, Feb 01, 2001 at 09:46:27PM +0100
Hi,
On Thu, Feb 01, 2001 at 09:46:27PM +0100, Christoph Hellwig wrote:
> > Right now we can take a kiobuf and turn it into a bunch of
> > buffer_heads for IO. The io_count lets us track all of those sub-IOs
> > so that we know when all submitted IO has completed, so that we can
> > pass the completion callback back up the chain without having to
> > allocate yet more descriptor structs for the IO.
>
> > Again, remove this and the IO becomes more heavyweight because we need
> > to create a separate struct for the info.
>
> No. Just allow passing the multiple of the devices blocksize over
> ll_rw_block.
That was just one example: you need the sub-ios just as much when
you split up an IO over stripe boundaries in LVM or raid0, for
example. Secondly, ll_rw_block needs to die anyway: you can expand
the blocksize up to PAGE_SIZE but not beyond, whereas something like
ll_rw_kiobuf can submit a much larger IO atomically (and we have
devices which don't start to deliver good throughput until you use
IO sizes of 1MB or more).
> >> and the lack of
> >> scatter gather in one kiobuf struct (you always need an array)
>
> > Again, _all_ data being sent down through the block device layer is
> > either in buffer heads or is page aligned.
>
> That's the point. You are always talking about the block-layer only.
I'm talking about why the minimal, generic solution doesn't provide
what the block layer needs.
> > Obviously, extra code will be needed to scan kiobufs if we do that,
> > and unless we have both per-page _and_ per-kiobuf start/offset pairs
> > (adding even further to the complexity), those scatter-gather lists
> > would prevent us from carving up a kiobuf into smaller sub-ios without
> > copying the whole (expanded) vector.
>
> No. I think I explained that in my last mail.
How?
If I've got a vector (page X, offset 0, length PAGE_SIZE) and I want
to split it in two, I have to make two new vectors (page X, offset 0,
length n) and (page X, offset n, length PAGE_SIZE-n). That implies
copying both vectors.
If I have a page vector with a single offset/length pair, I can build
a new header with the same vector and modified offset/length to split
the vector in two without copying it.
> > Possibly, but I remain to be convinced, because you may end up with a
> > mechanism which is generic but is not well-tuned for any specific
> > case, so everything goes slower.
>
> As kiobufs are widely used for real IO, just as containers, this is
> better then nothing.
Surely having all of the subsystems working fast is better still?
> And IMHO a nice generic concepts that lets different subsystems work
> toegther is a _lot_ better then a bunch of over-optimized, rather isolated
> subsytems. The IO-Lite people have done a nice research of the effect of
> an unified IO-Caching system vs. the typical isolated systems.
I know, and IO-Lite has some major problems (the close integration of
that code into the cache, for example, makes it harder to expose the
zero-copy to user-land).
--Stephen
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next prev parent reply other threads:[~2001-02-01 21:27 UTC|newest]
Thread overview: 201+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-02-01 14:44 [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait /notify + callback chains bsuparna
2001-02-01 15:09 ` Christoph Hellwig
2001-02-01 16:08 ` Steve Lord
2001-02-01 16:49 ` Stephen C. Tweedie
2001-02-01 17:02 ` Christoph Hellwig
2001-02-01 17:34 ` Alan Cox
2001-02-01 17:49 ` Stephen C. Tweedie
2001-02-01 17:09 ` Chaitanya Tumuluri
2001-02-01 20:33 ` Christoph Hellwig
2001-02-01 20:56 ` Steve Lord
2001-02-01 20:59 ` Christoph Hellwig
2001-02-01 21:17 ` Steve Lord
2001-02-01 21:44 ` Stephen C. Tweedie
2001-02-01 22:07 ` Stephen C. Tweedie
2001-02-02 12:02 ` Christoph Hellwig
2001-02-05 12:19 ` Stephen C. Tweedie
2001-02-05 21:28 ` Ingo Molnar
2001-02-05 22:58 ` Stephen C. Tweedie
2001-02-05 23:06 ` Alan Cox
2001-02-05 23:16 ` Stephen C. Tweedie
2001-02-06 0:19 ` Manfred Spraul
2001-02-03 20:28 ` Linus Torvalds
2001-02-05 11:03 ` Stephen C. Tweedie
2001-02-05 12:00 ` Manfred Spraul
2001-02-05 15:03 ` Stephen C. Tweedie
2001-02-05 15:19 ` Alan Cox
2001-02-05 17:20 ` Stephen C. Tweedie
2001-02-05 17:29 ` Alan Cox
2001-02-05 18:49 ` Stephen C. Tweedie
2001-02-05 19:04 ` Alan Cox
2001-02-05 19:09 ` Linus Torvalds
2001-02-05 19:16 ` [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait Alan Cox
2001-02-05 19:28 ` Linus Torvalds
2001-02-05 20:54 ` Stephen C. Tweedie
2001-02-05 21:08 ` David Lang
2001-02-05 21:51 ` Alan Cox
2001-02-06 0:07 ` Stephen C. Tweedie
2001-02-06 17:00 ` Christoph Hellwig
2001-02-06 17:05 ` Stephen C. Tweedie
2001-02-06 17:14 ` Jens Axboe
2001-02-06 17:22 ` Christoph Hellwig
2001-02-06 18:26 ` Stephen C. Tweedie
2001-02-06 17:37 ` Ben LaHaise
2001-02-06 18:00 ` Jens Axboe
2001-02-06 18:09 ` Ben LaHaise
2001-02-06 19:35 ` Jens Axboe
2001-02-06 18:14 ` Linus Torvalds
2001-02-08 11:21 ` Andi Kleen
2001-02-08 14:11 ` Martin Dalecki
2001-02-08 17:59 ` Linus Torvalds
2001-02-06 18:18 ` Ingo Molnar
2001-02-06 18:25 ` Ben LaHaise
2001-02-06 18:35 ` Ingo Molnar
2001-02-06 18:54 ` Ben LaHaise
2001-02-06 18:58 ` Ingo Molnar
2001-02-06 19:11 ` Ben LaHaise
2001-02-06 19:32 ` Jens Axboe
2001-02-06 19:32 ` Ingo Molnar
2001-02-06 19:32 ` Linus Torvalds
2001-02-06 19:44 ` Ingo Molnar
2001-02-06 19:49 ` Ben LaHaise
2001-02-06 19:57 ` Ingo Molnar
2001-02-06 20:07 ` Jens Axboe
2001-02-06 20:25 ` Ben LaHaise
2001-02-06 20:41 ` Manfred Spraul
2001-02-06 20:50 ` Jens Axboe
2001-02-06 21:26 ` Manfred Spraul
2001-02-06 21:42 ` Linus Torvalds
2001-02-06 20:16 ` Marcelo Tosatti
2001-02-06 22:09 ` Jens Axboe
2001-02-06 22:26 ` Linus Torvalds
2001-02-06 21:13 ` Marcelo Tosatti
2001-02-06 23:26 ` Linus Torvalds
2001-02-07 23:17 ` select() returning busy for regular files [was Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait] Pavel Machek
2001-02-08 13:57 ` Ben LaHaise
2001-02-08 17:52 ` Linus Torvalds
2001-02-08 15:06 ` [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait Ben LaHaise
2001-02-08 13:44 ` Marcelo Tosatti
2001-02-08 13:45 ` Marcelo Tosatti
2001-02-07 23:15 ` Pavel Machek
2001-02-08 13:22 ` Stephen C. Tweedie
2001-02-08 12:03 ` Marcelo Tosatti
2001-02-08 15:46 ` Mikulas Patocka
2001-02-08 14:05 ` Marcelo Tosatti
2001-02-08 16:11 ` Mikulas Patocka
2001-02-08 14:44 ` Marcelo Tosatti
2001-02-08 16:57 ` Rik van Riel
2001-02-08 17:13 ` James Sutherland
2001-02-08 18:38 ` Linus Torvalds
2001-02-09 12:17 ` Martin Dalecki
2001-02-08 15:55 ` Jens Axboe
2001-02-08 18:09 ` Linus Torvalds
2001-02-08 14:52 ` Mikulas Patocka
2001-02-08 19:50 ` Stephen C. Tweedie
2001-02-11 21:30 ` Pavel Machek
2001-02-06 21:57 ` Manfred Spraul
2001-02-06 22:13 ` Linus Torvalds
2001-02-06 22:26 ` Andre Hedrick
2001-02-06 20:49 ` Jens Axboe
2001-02-07 0:21 ` Stephen C. Tweedie
2001-02-07 0:25 ` Ingo Molnar
2001-02-07 0:36 ` Stephen C. Tweedie
2001-02-07 0:50 ` Linus Torvalds
2001-02-07 1:49 ` Stephen C. Tweedie
2001-02-07 2:37 ` Linus Torvalds
2001-02-07 14:52 ` Stephen C. Tweedie
2001-02-07 19:12 ` Richard Gooch
2001-02-07 20:03 ` Stephen C. Tweedie
2001-02-07 1:51 ` Jeff V. Merkey
2001-02-07 1:01 ` Ingo Molnar
2001-02-07 1:59 ` Jeff V. Merkey
2001-02-07 1:02 ` Jens Axboe
2001-02-07 1:19 ` Linus Torvalds
2001-02-07 1:39 ` Jens Axboe
2001-02-07 1:45 ` Linus Torvalds
2001-02-07 1:55 ` Jens Axboe
2001-02-07 9:10 ` David Howells
2001-02-07 12:16 ` Stephen C. Tweedie
2001-02-07 2:00 ` Jeff V. Merkey
2001-02-07 1:06 ` Ingo Molnar
2001-02-07 1:09 ` Jens Axboe
2001-02-07 1:11 ` Ingo Molnar
2001-02-07 1:26 ` Linus Torvalds
2001-02-07 2:07 ` Jeff V. Merkey
2001-02-07 1:08 ` Jens Axboe
2001-02-07 2:08 ` Jeff V. Merkey
2001-02-07 1:42 ` Jeff V. Merkey
2001-02-07 0:42 ` Linus Torvalds
2001-02-07 0:35 ` Jens Axboe
2001-02-07 0:41 ` Linus Torvalds
2001-02-07 1:27 ` Stephen C. Tweedie
2001-02-07 1:40 ` Linus Torvalds
2001-02-12 10:07 ` Jamie Lokier
2001-02-06 20:26 ` Linus Torvalds
2001-02-06 20:25 ` Christoph Hellwig
2001-02-06 20:35 ` Ingo Molnar
2001-02-06 19:05 ` Marcelo Tosatti
2001-02-06 20:59 ` Ingo Molnar
2001-02-06 21:20 ` Steve Lord
2001-02-07 18:27 ` Christoph Hellwig
2001-02-06 20:59 ` Linus Torvalds
2001-02-07 18:26 ` Christoph Hellwig
2001-02-07 18:36 ` Linus Torvalds
2001-02-07 18:44 ` Christoph Hellwig
2001-02-08 0:34 ` Neil Brown
2001-02-06 19:46 ` Ingo Molnar
2001-02-06 20:16 ` Ben LaHaise
2001-02-06 20:22 ` Ingo Molnar
2001-02-06 19:20 ` Linus Torvalds
2001-02-06 0:31 ` Roman Zippel
2001-02-06 1:01 ` Linus Torvalds
2001-02-06 9:22 ` Roman Zippel
2001-02-06 9:30 ` Ingo Molnar
2001-02-06 1:08 ` David S. Miller
2001-02-05 22:09 ` [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait /notify + callback chains Ingo Molnar
2001-02-05 16:56 ` Linus Torvalds
2001-02-05 17:27 ` [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait Alan Cox
2001-02-05 16:36 ` [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait /notify + callback chains Linus Torvalds
2001-02-05 19:08 ` Stephen C. Tweedie
2001-02-01 17:49 ` Christoph Hellwig
2001-02-01 17:58 ` Alan Cox
2001-02-01 18:32 ` Rik van Riel
2001-02-01 18:59 ` yodaiken
2001-02-01 19:33 ` Stephen C. Tweedie
2001-02-01 18:51 ` bcrl
2001-02-01 16:16 ` Stephen C. Tweedie
2001-02-01 17:05 ` Christoph Hellwig
2001-02-01 17:09 ` Christoph Hellwig
2001-02-01 17:41 ` Stephen C. Tweedie
2001-02-01 18:14 ` Christoph Hellwig
2001-02-01 18:25 ` Alan Cox
2001-02-01 18:39 ` Rik van Riel
2001-02-01 18:46 ` [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait Alan Cox
2001-02-01 18:48 ` [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait /notify + callback chains Christoph Hellwig
2001-02-01 18:57 ` Alan Cox
2001-02-01 19:00 ` Christoph Hellwig
2001-02-01 19:32 ` Stephen C. Tweedie
2001-02-01 20:46 ` Christoph Hellwig
2001-02-01 21:25 ` Stephen C. Tweedie [this message]
2001-02-02 11:51 ` Christoph Hellwig
2001-02-02 14:04 ` Stephen C. Tweedie
2001-02-02 4:18 ` bcrl
2001-02-02 12:12 ` Christoph Hellwig
2001-02-01 20:04 ` Chaitanya Tumuluri
-- strict thread matches above, loose matches on Subject: below --
2001-02-06 13:50 bsuparna
2001-02-06 14:07 ` Jens Axboe
[not found] <CA2569EA.00506BBC.00@d73mta05.au.ibm.com>
2001-02-05 15:01 ` Stephen C. Tweedie
2001-02-05 14:31 bsuparna
[not found] <CA2569E9.004A4E23.00@d73mta05.au.ibm.com>
2001-02-05 12:09 ` Stephen C. Tweedie
2001-02-04 13:24 bsuparna
2001-02-02 15:31 bsuparna
2001-02-01 13:20 bsuparna
2001-02-01 7:58 bsuparna
2001-02-01 12:39 ` Stephen C. Tweedie
2001-02-01 4:55 bsuparna
2001-02-01 12:19 ` Stephen C. Tweedie
2001-02-01 16:30 ` Chaitanya Tumuluri
2001-02-01 3:59 bsuparna
[not found] <CA2569E5.004D51A7.00@d73mta05.au.ibm.com>
2001-01-31 23:32 ` Stephen C. Tweedie
2001-01-31 13:58 bsuparna
2001-01-30 14:09 bsuparna
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