linux-kernel - Re: [PATCH 2 of 4] Introduce i386 fibril scheduling

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Message-ID: <20070207000626.GC32307@ca-server1.us.oracle.com>
Date:	Tue, 6 Feb 2007 16:06:26 -0800
From:	Joel Becker <Joel.Becker@...cle.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Kent Overstreet <kent.overstreet@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Zach Brown <zach.brown@...cle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-aio@...ck.org, Suparna Bhattacharya <suparna@...ibm.com>,
	Benjamin LaHaise <bcrl@...ck.org>
Subject: Re: [PATCH 2 of 4] Introduce i386 fibril scheduling

On Tue, Feb 06, 2007 at 03:56:14PM -0800, Davide Libenzi wrote:
> Async syscall submissions are a _one time_ things. It's not like a live fd 
> that you can push inside epoll and avoid the multiple O(N) passes.
> First of all, the amount of syscalls that you'd submit in a vectored way 
> are limited. They do not depend on the total number of connections, but on 

	I regularly see apps that want to submit 1000 I/Os at once.
Every submit.  But it's all against one or two file descriptors.  So, if
you return to userspace, they have to walk all 1000 async_results every
time, just to see which completed and which didn't.  And *then* go wait
for the ones that didn't.  If they just wait for them all, they aren't
spinning cpu on the -EASYNC operations.
	I'm not saying that "don't return a completion if we can
non-block it" is inherently wrong or not a good idea.  I'm saying that
we need a way to flag them efficiently.

Joel

-- 

Life's Little Instruction Book #80

	"Slow dance"

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@...cle.com
Phone: (650) 506-8127
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