From: Nick Piggin <nickpiggin@yahoo.com.au>
To: unlisted-recipients:; (no To-header on input)
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Zach Brown <zach.brown@oracle.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-aio@kvack.org, Suparna Bhattacharya <suparna@in.ibm.com>,
Benjamin LaHaise <bcrl@kvack.org>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH 0 of 4] Generic AIO by scheduling stacks
Date: Wed, 31 Jan 2007 16:51:48 +1100 [thread overview]
Message-ID: <45C02E74.2050401@yahoo.com.au> (raw)
In-Reply-To: <45C02AFA.4080501@yahoo.com.au>
Nick Piggin wrote:
> Linus Torvalds wrote:
>
>>
>> On Wed, 31 Jan 2007, Benjamin Herrenschmidt wrote:
>>
>>
>>>> - We would now have some measure of task_struct concurrency. Read
>>>> that twice,
>>>> it's scary. As two fibrils execute and block in turn they'll each be
>>>> referencing current->. It means that we need to audit task_struct
>>>> to make sure
>>>> that paths can handle racing as its scheduled away. The current
>>>> implementation
>>>> *does not* let preemption trigger a fibril switch. So one only has
>>>> to worry
>>>> about racing with voluntary scheduling of the fibril paths. This
>>>> can mean
>>>> moving some task_struct members under an accessor that hides them in
>>>> a struct
>>>> in task_struct so they're switched along with the fibril. I think
>>>> this is a
>>>> manageable burden.
>>>
>>>
>>> That's the one scaring me in fact ... Maybe it will end up being an easy
>>> one but I don't feel too comfortable...
>>
>>
>>
>> We actually have almost zero "interesting" data in the task-struct.
>>
>> All the real meat of a task has long since been split up into
>> structures that can be shared for threading anyway (ie
>> signal/files/mm/etc).
>>
>> Which is why I'm personally very comfy with just re-using task_struct
>> as-is.
>>
>> NOTE! This is with the understanding that we *never* do any
>> preemption. The whole point of the microthreading as far as I'm
>> concerned is exactly that it is cooperative. It's not preemptive, and
>> it's emphatically *not* concurrent (ie you'd never have two fibrils
>> running at the same time on separate CPU's).
>
>
> So using stacks to hold state is (IMO) the logical choice to do async
> syscalls, especially once you have a look at some of the other AIO
> stuff going around.
>
> I always thought that the AIO people didn't do this because they wanted
> to avoid context switch overhead.
>
> So now if we introduce the context switch overhead back, why do we need
> just another scheduling primitive? What's so bad about using threads? The
> upside is that almost everything is already there and working, and also
> they don't have any of these preemption or concurrency restrictions.
In other words, while I share the appreciation for this clever trick of
using cooperative switching between these little thriblets, I don't
actually feel it is very elegant to then have to change the kernel so
much in order to handle them.
I would be fascinated to see where such a big advantage comes from using
these rather than threads. Maybe we can then improve threads not to suck
so much and everybody wins.
--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com
next prev parent reply other threads:[~2007-01-31 5:52 UTC|newest]
Thread overview: 151+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-30 20:39 [PATCH 0 of 4] Generic AIO by scheduling stacks Zach Brown
2007-01-30 20:39 ` [PATCH 1 of 4] Introduce per_call_chain() Zach Brown
2007-01-30 20:39 ` [PATCH 2 of 4] Introduce i386 fibril scheduling Zach Brown
2007-02-01 8:36 ` Ingo Molnar
2007-02-01 13:02 ` Ingo Molnar
2007-02-01 13:19 ` Christoph Hellwig
2007-02-01 13:52 ` Ingo Molnar
2007-02-01 17:13 ` Mark Lord
2007-02-01 18:02 ` Ingo Molnar
2007-02-02 13:23 ` Andi Kleen
2007-02-01 21:52 ` Zach Brown
2007-02-01 22:23 ` Benjamin LaHaise
2007-02-01 22:37 ` Zach Brown
2007-02-02 13:22 ` Andi Kleen
2007-02-01 20:07 ` Linus Torvalds
2007-02-02 10:49 ` Ingo Molnar
2007-02-02 15:56 ` Linus Torvalds
2007-02-02 19:59 ` Alan
2007-02-02 20:14 ` Linus Torvalds
2007-02-02 20:58 ` Davide Libenzi
2007-02-02 21:09 ` Linus Torvalds
2007-02-02 21:30 ` Alan
2007-02-02 21:30 ` Linus Torvalds
2007-02-02 22:42 ` Ingo Molnar
2007-02-02 23:01 ` Linus Torvalds
2007-02-02 23:17 ` Linus Torvalds
2007-02-03 0:04 ` Alan
2007-02-03 0:23 ` bert hubert
2007-02-02 22:48 ` Alan
2007-02-05 16:44 ` Zach Brown
2007-02-02 22:21 ` Ingo Molnar
2007-02-02 22:49 ` Linus Torvalds
2007-02-02 23:55 ` Ingo Molnar
2007-02-03 0:56 ` Linus Torvalds
2007-02-03 7:15 ` Suparna Bhattacharya
2007-02-03 8:23 ` Ingo Molnar
2007-02-03 9:25 ` Matt Mackall
2007-02-03 10:03 ` Ingo Molnar
2007-02-05 17:44 ` Zach Brown
2007-02-05 19:26 ` Davide Libenzi
2007-02-05 19:41 ` Zach Brown
2007-02-05 20:10 ` Davide Libenzi
2007-02-05 20:21 ` Zach Brown
2007-02-05 20:42 ` Linus Torvalds
2007-02-05 20:39 ` Linus Torvalds
2007-02-05 21:09 ` Davide Libenzi
2007-02-05 21:31 ` Kent Overstreet
2007-02-06 20:25 ` Davide Libenzi
2007-02-06 20:46 ` Linus Torvalds
2007-02-06 21:16 ` David Miller
2007-02-06 21:28 ` Linus Torvalds
2007-02-06 21:31 ` David Miller
2007-02-06 21:46 ` Eric Dumazet
2007-02-06 21:50 ` Linus Torvalds
2007-02-06 22:28 ` Zach Brown
2007-02-06 22:45 ` Kent Overstreet
2007-02-06 23:04 ` Linus Torvalds
2007-02-07 1:22 ` Kent Overstreet
2007-02-06 23:23 ` Davide Libenzi
2007-02-06 23:39 ` Joel Becker
2007-02-06 23:56 ` Davide Libenzi
2007-02-07 0:06 ` Joel Becker
2007-02-07 0:23 ` Davide Libenzi
2007-02-07 0:44 ` Joel Becker
2007-02-07 1:15 ` Davide Libenzi
2007-02-07 1:24 ` Kent Overstreet
2007-02-07 1:30 ` Joel Becker
2007-02-07 6:16 ` Michael K. Edwards
2007-02-07 9:17 ` Michael K. Edwards
2007-02-07 9:37 ` Michael K. Edwards
2007-02-06 0:32 ` Davide Libenzi
2007-02-05 21:21 ` Zach Brown
2007-02-02 23:37 ` Davide Libenzi
2007-02-03 0:02 ` Davide Libenzi
2007-02-05 17:12 ` Zach Brown
2007-02-05 18:24 ` Davide Libenzi
2007-02-05 21:44 ` David Miller
2007-02-06 0:15 ` Davide Libenzi
2007-02-05 21:36 ` bert hubert
2007-02-05 21:57 ` Linus Torvalds
2007-02-05 22:07 ` bert hubert
2007-02-05 22:15 ` Zach Brown
2007-02-05 22:34 ` Davide Libenzi
2007-02-06 0:27 ` Scot McKinley
2007-02-06 0:48 ` David Miller
2007-02-06 0:48 ` Joel Becker
2007-02-05 17:02 ` Zach Brown
2007-02-05 18:52 ` Davide Libenzi
2007-02-05 19:20 ` Zach Brown
2007-02-05 19:38 ` Davide Libenzi
2007-02-04 5:12 ` Davide Libenzi
2007-02-05 17:54 ` Zach Brown
2007-01-30 20:39 ` [PATCH 3 of 4] Teach paths to wake a specific void * target instead of a whole task_struct Zach Brown
2007-01-30 20:39 ` [PATCH 4 of 4] Introduce aio system call submission and completion system calls Zach Brown
2007-01-31 8:58 ` Andi Kleen
2007-01-31 17:15 ` Zach Brown
2007-01-31 17:21 ` Andi Kleen
2007-01-31 19:23 ` Zach Brown
2007-02-01 11:13 ` Suparna Bhattacharya
2007-02-01 19:50 ` Trond Myklebust
2007-02-02 7:19 ` Suparna Bhattacharya
2007-02-02 7:45 ` Andi Kleen
2007-02-01 22:18 ` Zach Brown
2007-02-02 3:35 ` Suparna Bhattacharya
2007-02-01 20:26 ` bert hubert
2007-02-01 21:29 ` Zach Brown
2007-02-02 7:12 ` bert hubert
2007-02-04 5:12 ` Davide Libenzi
2007-01-30 21:58 ` [PATCH 0 of 4] Generic AIO by scheduling stacks Linus Torvalds
2007-01-30 22:23 ` Linus Torvalds
2007-01-30 22:53 ` Zach Brown
2007-01-30 22:40 ` Zach Brown
2007-01-30 22:53 ` Linus Torvalds
2007-01-30 23:45 ` Zach Brown
2007-01-31 2:07 ` Benjamin Herrenschmidt
2007-01-31 2:04 ` Benjamin Herrenschmidt
2007-01-31 2:46 ` Linus Torvalds
2007-01-31 3:02 ` Linus Torvalds
2007-01-31 10:50 ` Xavier Bestel
2007-01-31 19:28 ` Zach Brown
2007-01-31 17:59 ` Zach Brown
2007-01-31 5:16 ` Benjamin Herrenschmidt
2007-01-31 5:36 ` Nick Piggin
2007-01-31 5:51 ` Nick Piggin [this message]
2007-01-31 6:06 ` Linus Torvalds
2007-01-31 8:43 ` Ingo Molnar
2007-01-31 20:13 ` Joel Becker
2007-01-31 18:20 ` Zach Brown
2007-01-31 17:47 ` Zach Brown
2007-01-31 17:38 ` Zach Brown
2007-01-31 17:51 ` Benjamin LaHaise
2007-01-31 19:25 ` Zach Brown
2007-01-31 20:05 ` Benjamin LaHaise
2007-01-31 20:41 ` Zach Brown
2007-02-04 5:13 ` Davide Libenzi
2007-02-04 20:00 ` Davide Libenzi
2007-02-09 22:33 ` Linus Torvalds
2007-02-09 23:11 ` Davide Libenzi
2007-02-09 23:35 ` Linus Torvalds
2007-02-10 18:45 ` Davide Libenzi
2007-02-10 19:01 ` Linus Torvalds
2007-02-10 19:35 ` Linus Torvalds
2007-02-10 20:59 ` Davide Libenzi
2007-02-10 0:04 ` Eric Dumazet
2007-02-10 0:12 ` Linus Torvalds
2007-02-10 0:34 ` Alan
2007-02-10 10:47 ` bert hubert
2007-02-10 18:19 ` Davide Libenzi
2007-02-11 0:56 ` David Miller
2007-02-11 2:49 ` Linus Torvalds
2007-02-14 16:42 ` James Antill
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