Re: Approaches to making io_submit not block

[guy keren <choo@actcom.co.il>]

On Tue, 2011-08-30 at 15:54 -0700, Andrew Morton wrote:
> On Tue, 30 Aug 2011 15:45:35 -0700
> Daniel Ehrenberg <dehrenberg@google.com> wrote:
> 
> > >> Not quite sure, and after working on them and fixing thing up, I don't
> > >> even think they are that complex or intrusive (which I think otherwise
> > >> would've been the main objection). Andrew may know/remember.
> > >
> > > Boy, that was a long time ago. __I was always unhappy with the patches
> > > because of the amount of additional code/complexity they added.
> > >
> > > Then the great syslets/threadlets design session happened and it was
> > > expected that such a facility would make special async handling for AIO
> > > unnecessary. __Then syslets/threadlets didn't happen.
> > 
> > Do you think we could accomplish the goals with less additional
> > code/complexity? It looks like the latest version of the patch set
> > wasn't so invasive.
> > 
> > If syslets/threadlets aren't happening, should these patches be
> > reconsidered for inclusion in the kernel?
> 
> I haven't seen any demand at all for the feature in many years.  That
> doesn't mean that there _isn't_ any demand - perhaps everyone got
> exhausted.

you should consider the emerging enterprise-grade SSD devices - which
can serve several tens of thousands of I/O requests per device actually
controller). These devices could be better utilized by better
interfaces. further more, in our company we had to resort to using
windows for IOPS benchmarking (using iometer) against storage systems
using these (and similar) devices, because it manages to generate higher
IOPS then linux can (i don't remember the exact numbers, but we are
talking about an order of several hundred thousands IOPS).

It could be that we are currently an esoteric use-case - but the
high-end performance market seems to be stepping in that direction.

> If there is demand then that should be described and circulated, see
> how much interest there is in resurrecting the effort.
> 
> And, of course, the patches should be dragged out and looked at - it's
> been a number of years now.
> 
> Also, glibc has userspace for POSIX AIO.  A successful kernel-based
> implementation would result in glibc migrating away from its current
> implementation.  So we should work with the glibc developers on ensuring
> that the migration can happen.

glibc's userspace implementation doesn't scale to fast devices. It could
make sense when working with slower disk devices - not when you're
working with solid-state storage devices.

--guy