From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43491) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WJLI0-0007Ix-5l for qemu-devel@nongnu.org; Fri, 28 Feb 2014 06:07:41 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WJLHv-0002xK-DM for qemu-devel@nongnu.org; Fri, 28 Feb 2014 06:07:36 -0500 Received: from szxga01-in.huawei.com ([119.145.14.64]:15261) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WJLHu-0002x3-NR for qemu-devel@nongnu.org; Fri, 28 Feb 2014 06:07:31 -0500 Message-ID: <53106DCD.9000806@huawei.com> Date: Fri, 28 Feb 2014 19:06:53 +0800 From: Gonglei MIME-Version: 1.0 References: <33183CC9F5247A488A2544077AF19020815D229D@SZXEMA503-MBS.china.huawei.com> <20140228103022.GG2695@work-vm> In-Reply-To: <20140228103022.GG2695@work-vm> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 6/7] migraion: optimiztion xbzrle by reducing data copy List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Dr. David Alan Gilbert" Cc: "chenliang (T)" , Peter Maydell , Juan Quintela , "pl@kamp.de" , "qemu-devel@nongnu.org" , "aliguori@amazon.com" , "pbonzini@redhat.com" On 2014/2/28 18:30, Dr. David Alan Gilbert wrote: > * Gonglei (Arei) (arei.gonglei@huawei.com) wrote: >> Reducing data copy can reduce cpu overheah. > > (Note a few typos in subject/title) > >> Signed-off-by: ChenLiang >> Signed-off-by: Gonglei >> --- >> arch_init.c | 8 +++----- >> 1 file changed, 3 insertions(+), 5 deletions(-) >> >> diff --git a/arch_init.c b/arch_init.c >> index 2211e0b..cc88875 100644 >> --- a/arch_init.c >> +++ b/arch_init.c >> @@ -344,11 +344,8 @@ 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); >> - >> /* 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); > > Is xbzrle_encode_buffer safe if the main memory is still being changed while > it is run? Even with multiple CPUs changing it? Even on CPUs with looser > memory ordering semantics? > It's OK. We just need to assure the pages of cache and the pages which be sent coherence. >> if (encoded_len == 0) { >> @@ -367,7 +364,8 @@ 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 */ >> -- >> 1.7.12.4 >> >> >> Best regards, >> -Gonglei >> >> > -- > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK Best regards, -Gonglei