From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:36515)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <avi@redhat.com>) id 1Qtph0-00059h-Qv
	for qemu-devel@nongnu.org; Wed, 17 Aug 2011 19:38:39 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <avi@redhat.com>) id 1Qtpgz-0006tY-NO
	for qemu-devel@nongnu.org; Wed, 17 Aug 2011 19:38:38 -0400
Received: from mx1.redhat.com ([209.132.183.28]:12204)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <avi@redhat.com>) id 1Qtpgz-0006tU-FD
	for qemu-devel@nongnu.org; Wed, 17 Aug 2011 19:38:37 -0400
Message-ID: <4E4C50F6.20208@redhat.com>
Date: Wed, 17 Aug 2011 16:38:30 -0700
From: Avi Kivity <avi@redhat.com>
MIME-Version: 1.0
References: <cover.1313620857.git.jan.kiszka@web.de>
	<4da1c5e91e8f61b6c17aa0756006d030013bedd8.1313620857.git.jan.kiszka@web.de>
In-Reply-To: <4da1c5e91e8f61b6c17aa0756006d030013bedd8.1313620857.git.jan.kiszka@web.de>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH v2 5/6] vga: Use linear mapping + dirty
 logging in chain 4 memory access mode
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: Jan Kiszka <jan.kiszka@web.de>
Cc: Anthony Liguori <aliguori@us.ibm.com>, qemu-devel <qemu-devel@nongnu.org>, Gerd Hoffmann <kraxel@redhat.com>

On 08/17/2011 03:41 PM, Jan Kiszka wrote:
> From: Jan Kiszka<jan.kiszka@siemens.com>
>
> Most VGA memory access modes require MMIO handling as they demand weird
> logic to get a byte from or into the video RAM. However, there is one
> exception: chain 4 mode with all memory planes enabled for writing. This
> mode actually allows lineary mapping, which can then be combined with
> dirty logging to accelerate KVM.
>
> This patch accelerates specifically VBE accesses like they are used by
> grub in graphical mode. Not only the standard VGA adapter benefits from
> this, also vmware and spice in VGA mode.

Excellent, this slowness is very annoying.

>
> +static void vga_update_memory_access(VGACommonState *s)
> +{
> +    MemoryRegion *region, *old_region = s->chain4_alias;
> +    target_phys_addr_t base, offset, size;
> +
> +    s->chain4_alias = NULL;
> +
> +    if ((s->sr[0x02]&  0xf) == 0xf&&  s->sr[0x04]&  0x08) {
> +        offset = 0;
> +        switch ((s->gr[6]>>  2)&  3) {
> +        case 0:
> +            base = 0xa0000;
> +            size = 0x20000;
> +            break;
> +        case 1:
> +            base = 0xa0000;
> +            size = 0x10000;
> +            offset = s->bank_offset;
> +            break;
> +        case 2:
> +            base = 0xb0000;
> +            size = 0x8000;
> +            break;
> +        case 3:
> +            base = 0xb8000;
> +            size = 0x8000;
> +            break;
> +        }
> +        region = qemu_malloc(sizeof(*region));
> +        memory_region_init_alias(region, "vga.chain4",&s->vram, offset, size);
> +        memory_region_add_subregion_overlap(get_system_memory(), base,
> +                                            region, 2);

get_system_memory() has been excised from vga in batch 4 of my patches, 
please adjust.

> +        s->chain4_alias = region;
> +    }
> +    if (old_region) {
> +        memory_region_del_subregion(get_system_memory(), old_region);
> +        memory_region_destroy(old_region);
> +        qemu_free(old_region);
> +    }
> +}
> +
>

The mmio code has

             s->plane_updated |= mask; /* only used to detect font change */

aren't we losing it?  we could easily recover it via dirty logging.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.