Re: [Qemu-devel] [PATCH][RFC] Linux AIO support when using O_DIRECT

From: Anthony Liguori <anthony@codemonkey.ws>
To: Avi Kivity <avi@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org
Subject: Re: [Qemu-devel] [PATCH][RFC] Linux AIO support when using O_DIRECT
Date: Mon, 23 Mar 2009 12:14:58 -0500	[thread overview]
Message-ID: <49C7C392.3030001@codemonkey.ws> (raw)
In-Reply-To: <49C7B620.8030203@redhat.com>

Avi Kivity wrote:
>
> Instead of introducing yet another layer of indirection, you could add 
> block-raw-linux-aio, which would be registered before block-raw-posix 
> (which is realy block-raw-threadpool...), and resist a ->probe() if 
> caching is enabled.

block-raw-posix needs a major overhaul.  That's why I'm not even 
considering committing the patch as is.

I'd like to see the O_DIRECT bounce buffering removed in favor of the 
DMA API bouncing.  Once that happens, raw_read and raw_pread can 
disappear.  block-raw-posix becomes much simpler.

We would drop the signaling stuff and have the thread pool use an fd to 
signal.  The big problem with that right now is that it'll cause a 
performance regression for certain platforms until we have the IO thread 
in place.

Regards,

Anthony Liguori