From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sergey Zhukov Subject: Forking time in Xen Date: Mon, 18 Jun 2012 16:38:39 +0700 Message-ID: <1340012319.13742.114.camel@sergey> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org Hi, I repost this message from xen-users list following by others subscribers suggestions: I found an article about forking time for redis NoSQL database in different systems: http://redis.io/topics/latency ---------Quote------------------ Fork time in different systems Modern hardware is pretty fast to copy the page table, but Xen is not. The problem with Xen is not virtualization-specific, but Xen-specific. For instance using VMware or Virutal Box does not result into slow fork time. The following is a table that compares fork time for different Redis instance size. Data is obtained performing a BGSAVE and looking at the latest_fork_usec filed in the INFO command output. * Linux beefy VM on VMware 6.0GB RSS forked in 77 milliseconds (12.8 milliseconds per GB). * Linux running on physical machine (Unknown HW) 6.1GB RSS forked in 80 milliseconds (13.1 milliseconds per GB) * Linux running on physical machine (Xeon @ 2.27Ghz) 6.9GB RSS forked into 62 millisecodns (9 milliseconds per GB). * Linux VM on 6sync (KVM) 360 MB RSS forked in 8.2 milliseconds (23.3 millisecond per GB). * Linux VM on EC2 (Xen) 6.1GB RSS forked in 1460 milliseconds (239.3 milliseconds per GB). * Linux VM on Linode (Xen) 0.9GBRSS forked into 382 millisecodns (424 milliseconds per GB). As you can see a VM running on Xen has a performance hit that is between one order to two orders of magnitude. We believe this is a severe problem with Xen and we hope it will be addressed ASAP. ----------End of quote----------------- I made my own test with Xen 4.1 and Redis 2.4 with 7.04GB dataset. The test was performed on Intel Core I5 2500 processor unit. Forking time was about 1 sec or 151 ms/GB - it's faster then tests over Amazon EC2/Linode were mentioned in the article, but still much slower then VMWare or physical machines. Has anyone running with this issue? Or may be there is a way to tune Xen for less forking times? Sergey Zhukov