Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.

From: Dan Kegel (dank@alumni.caltech.edu)
Date: Fri Jan 12 2001 - 13:10:59 EST


Michael Rothwell (rothwell@holly-springs.nc.us) wrote:

> How about using fcntl(), O_ASYNC and SIGIO?

Don't think that's supported for disk files yet, at least by the
kernel. glibc does aio emulation with threads, which isn't great.

> Or maybe a broader question:
> what's the preferred/working way to do async file i/o on Linux?

SGI has done lots of work on this, using kernel threads;
they don't have a patch yet for 2.4.0, but they do support
2.2.17 and 2.4.0-test10.

TUX uses async I/O, I think, but it's inside the kernel.
I hear plans are afoot for giving userspace async I/O that
avoids creating threads; that should be more scalable than
SGI's approach, if it ever happens.

See http://www.kegel.com/c10k.html#aio for links and a few notes.
- Dan
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