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

From: Anthony Liguori <anthony@codemonkey.ws>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>,
	kvm-devel <kvm@vger.kernel.org>,
	qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool
Date: Thu, 11 Dec 2008 14:40:29 -0600	[thread overview]
Message-ID: <49417ABD.6020908@codemonkey.ws> (raw)
In-Reply-To: <20081211181116.GE6809@random.random>

Andrea Arcangeli wrote:
> 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...

io_submit blocks unless you use O_DIRECT for most filesystems that 
people care about.

This is why the current trends are toward kernel space thread pools.  It 
would be very difficult to modify every file system to support true 
asynchronous buffered IO.

Also, it's pretty clear that linux-aio doesn't have a strong future so I 
don't think it's very worthwhile to support.

Regards,

Anthony Liguori

Regards,

Anthony Liguori