From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59626) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xyecn-0001Nl-Sy for qemu-devel@nongnu.org; Wed, 10 Dec 2014 05:36:10 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xyeci-00006l-PN for qemu-devel@nongnu.org; Wed, 10 Dec 2014 05:36:05 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58754) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xyeci-00006c-Ii for qemu-devel@nongnu.org; Wed, 10 Dec 2014 05:36:00 -0500 From: Juan Quintela In-Reply-To: <1416830152-524-6-git-send-email-arei.gonglei@huawei.com> (arei gonglei's message of "Mon, 24 Nov 2014 19:55:51 +0800") References: <1416830152-524-1-git-send-email-arei.gonglei@huawei.com> <1416830152-524-6-git-send-email-arei.gonglei@huawei.com> Date: Wed, 10 Dec 2014 11:35:23 +0100 Message-ID: <87mw6vaj2s.fsf@elfo.elfo> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH RESEND for 2.3 5/6] migration: optimize xbzrle by reducing data copy Reply-To: quintela@redhat.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: arei.gonglei@huawei.com Cc: ChenLiang , weidong.huang@huawei.com, qemu-devel@nongnu.org, dgilbert@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, peter.huangpeng@huawei.com wrote: > From: ChenLiang > > Signed-off-by: ChenLiang > Signed-off-by: Gonglei > Reviewed-by: Dr. David Alan Gilbert > --- > arch_init.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/arch_init.c b/arch_init.c > index 846e4c5..0d0ba4a 100644 > --- a/arch_init.c > +++ b/arch_init.c > @@ -376,11 +376,8 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t **current_data, > > prev_cached_page = get_cached_data(XBZRLE.cache, current_addr); > > - /* save current buffer into memory */ > - memcpy(XBZRLE.current_buf, *current_data, TARGET_PAGE_SIZE); > - I think this is wrong. Remember that now migration is done in parallel with the guest running. If the guest modifies the page while we are encoding it, we end with a different contents in the cache and in the real page, and that causes corruption. This way, what we encoded is a "private copy of the page, so we don't have that problem". Makes sense? > /* XBZRLE encoding (if there is no overflow) */ > - encoded_len = xbzrle_encode_buffer(prev_cached_page, XBZRLE.current_buf, > + encoded_len = xbzrle_encode_buffer(prev_cached_page, *current_data, > TARGET_PAGE_SIZE, XBZRLE.encoded_buf, > TARGET_PAGE_SIZE); > if (encoded_len == 0) { > @@ -399,7 +396,8 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t **current_data, > > /* we need to update the data in the cache, in order to get the same data */ > if (!last_stage) { > - memcpy(prev_cached_page, XBZRLE.current_buf, TARGET_PAGE_SIZE); > + xbzrle_decode_buffer(XBZRLE.encoded_buf, encoded_len, prev_cached_page, > + TARGET_PAGE_SIZE); > } > > /* Send XBZRLE based compressed page */