From mboxrd@z Thu Jan  1 00:00:00 1970
From: OHMURA Kei <ohmura.kei@lab.ntt.co.jp>
Subject: Re: [PATCH] qemu-kvm: Speed up of the dirty-bitmap-traveling
Date: Wed, 10 Feb 2010 18:55:49 +0900
Message-ID: <4B7282A5.7090500@lab.ntt.co.jp>
References: <4B6BF06D.1090909@lab.ntt.co.jp> <4B70065B.1010401@redhat.com> <4B7130E9.7060809@lab.ntt.co.jp> <4B713839.30301@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-2022-JP
Content-Transfer-Encoding: 7bit
Cc: kvm@vger.kernel.org, qemu-devel@nongnu.org, mtosatti@redhat.com,
	ohmura.kei@lab.ntt.co.jp
To: Avi Kivity <avi@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from tama500.ecl.ntt.co.jp ([129.60.39.148]:40406 "EHLO
	tama500.ecl.ntt.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753475Ab0BJJ4L (ORCPT <rfc822;kvm@vger.kernel.org>);
	Wed, 10 Feb 2010 04:56:11 -0500
In-Reply-To: <4B713839.30301@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

> Please reuse the changelog when reposing a patch, this makes it easier
> for me to apply it.

Thanks.  Will follow it from next time.


> Should be a host long size, not guest. This will fail when running a
> 32-bit qemu-system-x86_64 binary.

Sorry. That was our mistake.


> Instead of using a nested loop if bitmap_ul[i] != 0, it is possible to
> use just a single loop (while (c>  0)), and process a long's worth of data.
>
> The only trickery is with big endian hosts, where the conversion from
> bit number to page number is a bit complicated.

To convert the bitmap from big endian to little endian, le_bswap macro in
bswap.h seems useful, which is now undefined.  What do you think about this
approach?

This is an example bitmap-traveling code using le_bswap:
     /* 
      * bitmap-traveling is faster than memory-traveling (for addr...) 
      * especially when most of the memory is not dirty.
      */
     for (i = 0; i < len; i++) {
        if (bitmap_ul[i] != 0) {
            c = le_bswap(bitmap_ul[i], HOST_LONG_BITS);
            while (c > 0) {
                j = ffsl(c) - 1;
                c &= ~(1ul << j);
                page_number = i * HOST_LONG_BITS + j;
                addr1 = page_number * TARGET_PAGE_SIZE;
                addr = offset + addr1;
                ram_addr = cpu_get_physical_page_desc(addr);
                cpu_physical_memory_set_dirty(ram_addr);
            }
         }
     }