>> I have been using OpenWrt to build HVM DomU guests under Xen for some >> time. From what I can tell, Xen's PVHVM drivers (namely, netfront and >> blkfront) are not available on my OpenWrt DomU guests, and thus the >> guests rely on the slower QEMU-based drivers. As a result, the network >> and disk performance of these DomU guests is not optimal. >> >> I did notice that Felix removed the Xen DomU subtarget in January. >> Would it be possible to return support for Xen's front-end virtual device >> drivers for use with HVM guests?
> I just checked the last kernel I built for x86/generic (not x86/64) > and looking at kernel config (inside builddir), I have, by default: > [...] > CONFIG_XEN_BLKDEV_FRONTEND=y [...] Luiz pointed out that some versions of LEDE seem to support the Xen PVHVM drivers, so I decided to investigate this. I looked at: x86-17.01.2: http://downloads.lede-project.org/releases/17.01.2/targets/x86/generic/lede-17.01.2-x86-generic-combined-ext4.img.gz x86_64-17.01.2: http://downloads.lede-project.org/releases/17.01.2/targets/x86/64/lede-17.01.2-x86-64-combined-ext4.img.gz x86-master: http://downloads.lede-project.org/snapshots/targets/x86/generic/lede-x86-generic-combined-ext4.img.gz x86_64-master: http://downloads.lede-project.org/snapshots/targets/x86/64/lede-x86-64-combined-ext4.img.gz Here is what I found: 1. Only x86-master seemed to provide the Xen PVHVM drivers. I checked this for each build using "dmesg | grep front". 2. There was a drastic difference in write performance between x86-master and the other builds. For each build, I built a Xen domain using the following configuration: name = "x86" memory = 1024 vcpus = 1 builder = "hvm" disk = [ "tap2:tapdisk:aio:/path/to/combined-ext4.img,xvda,w", "phy:/dev/mapper/luks-b89e45b3-9b0e-4bf4-965e-918af4085d03,xvdb,w" ] serial = "pty" I then mounted the second disk at /mnt from within the Xen guest and ran "time dd bs=16k count=131072 if=/dev/zero of=/mnt/test". I ran the test twice for each build. Here are my measurements: x86-17.01.2 (QEMU): 3:08 / 2:38 x86_64-17.01.2 (QEMU): 2:23 / 1:57 x86-master (PVHVM): 0:25 / 0:20 x86_64-master (QEMU): 1:54 / 2:02 I realize "dd" is not the best benchmarking tool, but the advantage of the PVHVM drivers is pretty stark. In the case of the builds which use QEMU, I did indeed see qemu-dm working hard on Dom0 while dd ran. Given this, can we compile the PVHVM drivers into both the x86-generic and x86_64 builds? -- Mike :wq _______________________________________________ Lede-dev mailing list Lede-dev@lists.infradead.org http://lists.infradead.org/mailman/listinfo/lede-dev
