From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33808) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b35Og-0005Lf-03 for qemu-devel@nongnu.org; Wed, 18 May 2016 13:36:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b35Oe-0007y5-OC for qemu-devel@nongnu.org; Wed, 18 May 2016 13:36:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37492) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b35Oe-0007xq-If for qemu-devel@nongnu.org; Wed, 18 May 2016 13:36:36 -0400 Date: Wed, 18 May 2016 18:36:33 +0100 From: "Richard W.M. Jones" Message-ID: <20160518173633.GG1683@redhat.com> References: <20160516150401.GC28935@redhat.com> <20160516165336.GD15256@stefanha-x1.localdomain> <20160516182508.GQ1683@redhat.com> <573C1414.1050608@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <573C1414.1050608@linux.intel.com> Subject: Re: [Qemu-devel] Question about vNVDIMM file format List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Xiao Guangrong Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, "Zhang, Haozhong" I thought you might be interested in some performance results, "hot off the presses". With DAX enabled, I see the following messages in the guest kernel logs, which I assume means it is working: [ 0.469364] EXT4-fs (pmem0): DAX enabled. Warning: EXPERIMENTAL, use at your own risk [ 0.469932] EXT4-fs (pmem0): mounting ext2 file system using the ext4 subsystem [ 0.470682] EXT4-fs (pmem0): mounted filesystem without journal. Opts: dax Enabling vNVDIMM + ext4.ko + DAX for the libguestfs appliance[1] root disk improves our boot+shutdown performance measure[2] by between 20 and 30 milliseconds, which is about 5% faster at the moment. I also wanted to know if memory usage is reduced. I ran `free -m' inside a freshly booted appliance. Without DAX: $ free -m total used free shared buff/cache available Mem: 485 3 451 1 30 465 Swap: 0 0 0 With DAX: $ free -m total used free shared buff/cache available Mem: 485 3 469 1 12 467 Swap: 0 0 0 I also wanted to know if qemu's memory usage is reduced. I captured the rusage.ru_maxrss of the qemu subprocess with and without DAX. The difference is only about 5 MB, which doesn't seem like very much to me. Perhaps I'm measuring this wrong. If you have better suggestions for measuring memory usage, please let me know. Rich. [1] http://libguestfs.org/guestfs-internals.1.html#architecture [2] http://libguestfs.org/guestfs-performance.1.html#baseline:-starting-the-appliance -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW