linux-kernel - Re: [PATCH 4 of 4] Introduce aio system call submission and completion system calls

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Message-Id: <200701311821.59579.ak@suse.de>
Date:	Wed, 31 Jan 2007 18:21:59 +0100
From:	Andi Kleen <ak@...e.de>
To:	Zach Brown <zach.brown@...cle.com>
Cc:	linux-kernel@...r.kernel.org, linux-aio@...ck.org,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 4 of 4] Introduce aio system call submission and completion system calls

On Wednesday 31 January 2007 18:15, Zach Brown wrote:
> 
> On Jan 31, 2007, at 12:58 AM, Andi Kleen wrote:
> 
> > Do you have any numbers how this compares cycle wise to just doing
> > clone+syscall+exit in user space?
> 
> Not yet, no.  Release early, release often, and all that.  I'll throw  
> something together.

So what was the motivation for doing this then?  It's only point 
is to have smaller startup costs for AIO than clone+fork without
fixing the VFS code to be a state machine, right? 

I'm personally unclear if it's really less work to teach a lot of 
code in the kernel about a new thread abstraction than changing VFS.

Your patches don't look that complicated yet but you openly
admitted you waved away many of the more tricky issues (like 
signals etc.) and I bet there are yet-unknown side effects
of this too that will need more changes.

I would expect a VFS solution to be the fastest of any at least.

I'm not sure the fibrils thing will be that much faster than
a possibly somewhat fast pathed for this case clone+syscall+exit.

-Andi
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