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

[Joel Becker <Joel.Becker@oracle.com>]

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@oracle.com
Phone: (650) 506-8127