netdev - Re: [take36 10/10] kevent: Kevent based generic AIO.

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Date:	12 Feb 2007 14:08:10 +0100
From:	Andi Kleen <ak@...e.de>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	David Miller <davem@...emloft.net>,
	Ulrich Drepper <drepper@...hat.com>,
	Andrew Morton <akpm@...l.org>, netdev <netdev@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Chase Venters <chase.venters@...entec.com>,
	Johann Borck <johann.borck@...sedata.com>,
	linux-kernel@...r.kernel.org, Jeff Garzik <jeff@...zik.org>,
	Jamal Hadi Salim <hadi@...erus.ca>,
	Ingo Molnar <mingo@...e.hu>, linux-fsdevel@...r.kernel.org
Subject: Re: [take36 10/10] kevent: Kevent based generic AIO.

Evgeniy Polyakov <johnpol@....mipt.ru> writes:
> 
> aio_sendfile_path() is essentially aio_sendfile(), except that it takes
> source filename as parameter, has a pointer to private header
> and its size (which allows to send header and file's content in one syscall
> instead of three (open, send, sendfile) and returns opened file descriptor.

Are you sure this is a useful optimization? Do you have numbers vs open+aio_sendfile+close? 

Compared to the cost of sending a complete file three system calls should be quite in the noise. 
And Linux system calls are not that expensive (few hundred cycles normally) 

Adding such compound system calls would be a worrying precedent because
I'm sure others would want them then for their favourite system call combo
too. If they were really useful it might make more sense to have a batch() 
system call that works for arbitary calls, but I'm not convinced yet
it's even needed. It would be certainly ugly.

-Andi
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