From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:46173)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1TsDAG-0006Z4-2n
	for qemu-devel@nongnu.org; Mon, 07 Jan 2013 08:54:57 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1TsDAF-00038Y-0x
	for qemu-devel@nongnu.org; Mon, 07 Jan 2013 08:54:56 -0500
Received: from mail-bk0-f41.google.com ([209.85.214.41]:61175)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1TsDAE-00038T-Pk
	for qemu-devel@nongnu.org; Mon, 07 Jan 2013 08:54:54 -0500
Received: by mail-bk0-f41.google.com with SMTP id jg9so8394265bkc.14
	for <qemu-devel@nongnu.org>; Mon, 07 Jan 2013 05:54:53 -0800 (PST)
Date: Mon, 7 Jan 2013 14:54:50 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130107135450.GF17997@stefanha-thinkpad.redhat.com>
References: <20130105120511.388913E403B@msa101.auone-net.jp>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20130105120511.388913E403B@msa101.auone-net.jp>
Subject: Re: [Qemu-devel] [PATCH] raw-posix: Support discard on more
 filesystems
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Kusanagi Kouichi <slash@ac.auone-net.jp>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Sat, Jan 05, 2013 at 09:05:10PM +0900, Kusanagi Kouichi wrote:
> @@ -1098,15 +1101,30 @@ static int xfs_discard(BDRVRawState *s, int64_t sector_num, int nb_sectors)
>  static coroutine_fn int raw_co_discard(BlockDriverState *bs,
>      int64_t sector_num, int nb_sectors)
>  {
> -#ifdef CONFIG_XFS
> +#if defined(CONFIG_FALLOCATE_PUNCH_HOLE) || defined(CONFIG_XFS)
>      BDRVRawState *s = bs->opaque;
> +#endif
> +    int ret = 0;
>  
> +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
> +    do {
> +        if (fallocate(s->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> +                      sector_num << BDRV_SECTOR_BITS,
> +                      nb_sectors << BDRV_SECTOR_BITS) == 0) {
> +            return 0;
> +        }
> +    } while (errno == EINTR);

Is fallocate(fd, FALLOC_FL_PUNCH_HOLE) a blocking operation?

If yes, we need to perform this call in an aio worker thread (see
read/write/flush/ioctl in block/raw-posix.c).  Failure to do this means
QEMU and the guest will be blocked during fallocate and this causes poor
performance.

Stefan