From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH] qemu-kvm: clear only essential parts of VirtIOBlockReq
 on 	object allocation
Date: Sun, 08 Nov 2009 15:07:29 +0200
Message-ID: <4AF6C291.90204@redhat.com>
References: <41be791c0911040941y3548de23v20959cf1c1300875@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Cc: kvm@vger.kernel.org
To: Saul Tamari <stamari@gmail.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:19827 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752968AbZKHNHZ (ORCPT <rfc822;kvm@vger.kernel.org>);
	Sun, 8 Nov 2009 08:07:25 -0500
In-Reply-To: <41be791c0911040941y3548de23v20959cf1c1300875@mail.gmail.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On 11/04/2009 07:41 PM, Saul Tamari wrote:
> This patch reduces the size of memory being cleared on every virtio-blk IO.
>
> On every virtio-blk IO passed to QEMU, virtio_blk_alloc_request()
> allocates and clears (with qemu_mallocz()) a VirtIOBlockReq object.
> The sizeof(VirtIOBlockReq) equals 41040 bytes on my x86-64 machine.
> By moving the 'elem' variable to the end of VirtIOBlockReq and
> clearing only upto the address of the 'elem.in_addr' field, the
> memset() call now clears only 80 bytes.
>
>
> Signed-off-by: Saul Tamari<st...@gmail.com>
>    

Use the full email in signoffs.

> @@ -79,12 +79,12 @@ static inline void virtio_identify_template(struct
> virtio_blk_config *bc)
>   typedef struct VirtIOBlockReq
>   {
>       VirtIOBlock *dev;
> -    VirtQueueElement elem;
>       struct virtio_blk_inhdr *in;
>       struct virtio_blk_outhdr *out;
>       struct virtio_scsi_inhdr *scsi;
>       QEMUIOVector qiov;
>       struct VirtIOBlockReq *next;
> +    VirtQueueElement elem;
>   } VirtIOBlockReq;
>    

Needs a comment to indicate new members must be before 'elem' if they 
need to be cleared.

>   static void virtio_blk_req_complete(VirtIOBlockReq *req, int status)
> @@ -139,7 +139,8 @@ static void virtio_blk_flush_complete(void *opaque, int ret)
>
>   static VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s)
>   {
> -    VirtIOBlockReq *req = qemu_mallocz(sizeof(*req));
> +    VirtIOBlockReq *req = qemu_malloc(sizeof(*req));
> +    memset(req, 0, (size_t)&(((VirtIOBlockReq*)0)->elem.in_addr[0]));
>    

Please use offsetof() instead of open-coding it.

Submit to qemu-devel@nongnu.org since this came from upstream.

-- 
error compiling committee.c: too many arguments to function