From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59054) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eJDNN-0007XQ-2g for qemu-devel@nongnu.org; Mon, 27 Nov 2017 01:58:46 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eJDNI-0006vv-47 for qemu-devel@nongnu.org; Mon, 27 Nov 2017 01:58:45 -0500 Received: from mail-db5eur01on0057.outbound.protection.outlook.com ([104.47.2.57]:31200 helo=EUR01-DB5-obe.outbound.protection.outlook.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eJDNH-0006t8-Ix for qemu-devel@nongnu.org; Mon, 27 Nov 2017 01:58:40 -0500 Date: Mon, 27 Nov 2017 14:58:29 +0800 From: Dennis Chen Message-ID: <20171127065828.GA23555@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline Subject: [Qemu-devel] Question about RNG virtio device List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: dennis.chen@arm.com, nd@arm.com Hello QEMU developers, We all know that there is a virtio-rng device can be para-virtualised from the host to guest in case of a real RNG HW exists in the host, my question is: Can we get some performance gain to use the 'virtio-rng' device if there isn't a real RNG HW in host, in this case, what's the default back-end of the virtio -rng device? For my scenario, I don't want to use a virtio-rng device if the host doesn't have a RNG HW, because the guest will get a fake RNG HW with virtio-rng device (/sys/ devices/virtual/misc/hw_random/rng_current), which is not expected. But if virtio-rng is not used, I don't know how the guest get the entropy from the host, the most concern is performance. IOW, what's the difference between virtio-rng used and not if there isn't a RNG HW in host? Thanks!