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Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool

From: Andrea Arcangeli
Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool
Date: Thu, 11 Dec 2008 19:11:16 +0100

On Thu, Dec 11, 2008 at 06:20:09PM +0100, Gerd Hoffmann wrote:
> Andrea Arcangeli wrote:
> > On Thu, Dec 11, 2008 at 05:11:08PM +0100, Gerd Hoffmann wrote:
> >> Yes.  But kernel aio requires O_DIRECT, so aio users are affected
> >> nevertheless.
> > 
> > Are you sure? It surely wasn't the case...
> Tons of docs say so, but might be they are wrong, I didn't check.

I guess those tons of docs are just wrong then ;). I see no mention of
O_DIRECT in `man io_submit` at least... I seem to recall initially aio
only worked without O_DIRECT... ;). It's quite the opposite, O_DIRECT
works best with kernel aio, not the other way around. O_DIRECT
read/writes look very much like non-O_DIRECT seeking reads. For
seeking sync-reads kernel aio pays off as well as with O_DIRECT.

> So one could be preadv+threads.  Probably quite portable if we manage to
> get the syscalls into linux kernel and glibc.  All *BSDs have it
> already, for solaris I've found a feature request on that.  Dunno for MacOS.

Who's taking care of submitting it to linux?

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