From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1LApD5-0003ja-Ic
	for qemu-devel@nongnu.org; Thu, 11 Dec 2008 12:20:23 -0500
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1LApD2-0003i6-6b
	for qemu-devel@nongnu.org; Thu, 11 Dec 2008 12:20:23 -0500
Received: from [199.232.76.173] (port=39204 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1LApD1-0003hs-WD
	for qemu-devel@nongnu.org; Thu, 11 Dec 2008 12:20:20 -0500
Received: from mx2.redhat.com ([66.187.237.31]:45602)
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <kraxel@redhat.com>) id 1LApD1-0002IJ-0v
	for qemu-devel@nongnu.org; Thu, 11 Dec 2008 12:20:19 -0500
Message-ID: <49414BC9.5090905@redhat.com>
Date: Thu, 11 Dec 2008 18:20:09 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool
References: <493E965E.5050701@us.ibm.com>
	<20081210164401.GF18814@random.random>
	<493FFAB6.2000106@codemonkey.ws> <493FFC8E.9080802@redhat.com>
	<49400F69.8080707@codemonkey.ws>
	<20081210190810.GG18814@random.random>
	<20081211131222.GA14908@random.random>
	<494130B5.2080800@redhat.com>
	<20081211155335.GE14908@random.random>
	<49413B9C.3030703@redhat.com> <20081211164947.GD6809@random.random>
In-Reply-To: <20081211164947.GD6809@random.random>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: kvm-devel <kvm@vger.kernel.org>, qemu-devel@nongnu.org

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.

>> Kernel side looks easy, attached patch + syscall table windup in all
>> archs ...
> 
> So should we depend on this?

I suspect we will end up with multiple implementations anyway.

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.

Additionally we could have OS-specific bits such as linux-aio.  Maybe
also posix-aio for the *BSD family in case their kernel support for that
is better than what glibc provides (i.e. can handle multiple requests in
parallel without the fdpool hack).

cheers,
  Gerd