On Oct 13, 2009 at 0145 +0400, Michael Tokarev appeared and said: > René Pfeiffer wrote: > >Hello! > > > >I just tested qemu-kvm-0.11.0 with the KVM module of kernel 2.6.31.1. I > >noticed that the I/O performance of an unattended stock Debian Lenny > >install dropped somehow. The test machines ran with kvm-88 and 2.6.30.x > >before. The difference is very noticeable (went from about 5 minutes up > >to 15-25 minutes). The two test machines have different CPUs (one is an > >Intel Core2 CPU, the other runs with an AMD Athlon 64 X2 Dual). > > > >Is this the effect of added code regarding caching/data integrity to the > >VirtIO block layer or somewhere else? The qemu-system-x86_64 seems to > >hang a lot more in heavy I/O (showing 'D' in top/htop). > > > >The command line is quite straight-forward: > >qemu-system-x86_64 -drive file=debian.qcow2,if=virtio,boot=on -cdrom \ > >/srv/isos/debian-502-i386-netinst.iso -smp 2 -boot d -m 512 -net nic \ > >-net user -usb > ^^^^^^^^^ > > Care to try with something more real than user-level networking? Yes, I tried that on the other machine. It made not much difference (the installation files are on local Squid proxies). But I found that setting cache=writeback restores the old behaviour. I think the default changed to cache=writethrough. > You're using netinstall which - apparently - tries to use some > networking d/loading components etc, and userlevel networking is > known to be very very slow.... Right, I just verified the disk I/O performance with severall runs of hdparm and fresh installations using cache=none, cache=writeback and cache=writethrough settings. The network settings were the same (the test machine with the software bridge setup is down at the moment). I wanted to compare the behaviour of the I/O load. Best, René. -- )\._.,--....,'``. fL Let GNU/Linux work for you while you take a nap. /, _.. \ _\ (`._ ,. R. Pfeiffer <lynx at luchs.at> + http://web.luchs.at/ `._.-(,_..'--(,_..'`-.;.' - System administration + Consulting + Teaching - Got mail delivery problems? http://web.luchs.at/information/blockedmail.php
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