linux-kernel - Re: Syslets, Threadlets, generic AIO support, v6

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Message-ID: <465DE2BB.2060608@cosmosbay.com>
Date:	Wed, 30 May 2007 22:46:51 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Mark Lord <lkml@....ca>, Ingo Molnar <mingo@...e.hu>,
	Jeff Garzik <jeff@...zik.org>,
	Zach Brown <zach.brown@...cle.com>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Syslets, Threadlets, generic AIO support, v6

Linus Torvalds a écrit :
> 
> On Wed, 30 May 2007, Eric Dumazet wrote:
>> So yes, reimplement sendfile() should help to find last splice() bugs, and as
>> a bonus it could add non blocking disk io, (O_NONBLOCK on input file ->
>> socket)
> 
> Well, to get those kinds of advantages, you'd have to use splice directly, 
> since sendfile() hasn't supported nonblocking disk IO, and the interface 
> doesn't really allow for it.

sendfile() interface doesnt allow it, but if you open("somediskfile", O_RDONLY 
| O_NONBLOCK), then splice() based sendfile() can perform a non blocking disk 
io, (while starting an io with readahead)

I actually use this trick myself :)

(splice(disk -> pipe, NONBLOCK), splice(pipe -> worker))

non blocking disk io, + zero copy :)

> 
> In fact, since nonblocking accesses require also some *polling* method, 
> and we don't have that for files, I suspect the best option for those 
> things is to simply mix AIO and splice(). AIO tends to be the right thing 
> for disk waits (read: short, often cached), and if we can improve AIO 
> performance for the cached accesses (which is exactly what the threadlets 
> should hopefully allow us to do), I would seriously suggest going that 
> route.
> 
> But the pure "use splice to _implement_ sendfile()" thing is worth doing 
> for all the other reasons, even if nonblocking file access is not likely 
> one of them.
> 
> 		Linus
> 
> 

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