Bugs item #2926083, was opened at 2010-01-05 08:16 Message generated for change (Tracker Item Submitted) made by bakaproject You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=893831&aid=2926083&group_id=180599 Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: qemu Group: None Status: Open Resolution: None Priority: 5 Private: No Submitted By: Baka Project (bakaproject) Assigned to: Nobody/Anonymous (nobody) Summary: qcow2 default cache slows 0.12.1.2 vs kvm-88 Initial Comment: An install of a linux guest closely resembling RHEL5.4 x86_64 (Linux rats1 2.6.18-164.6.1.el5 #1 SMP Tue Oct 27 11:28:30 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux) is extremely slow in 0.12.1.2 compared to kvm-88. Some extensive git bisecting revealed the problem being that the default cache strategy for qcow2 was changed from writeback to writethrough. When I run qemu in writeback mode, the performance is restored. I understand the performance/correctness tradeoff here--after wasting a day tracking it down. I guess this is a plea to restore the previous behavior or better advertise the change or potential solutions to the problem. qemu command (without explicit cache): aoss x86_64-softmmu/qemu-system-x86_64 -enable-kvm -name rats2 -hda /VMs/images/rats2.cow -m 650 -monitor telnet:localhost:9008,server,nowait,nodelay -vnc :8 -cdrom /VMs/cds/curodw.iso -boot dc -net nic,model=rtl8139,macaddr=2e:2e:2e:0:0:db,vlan=0 -net tap,ifname=rats2_0,vlan=0,script=no,downscript=no -net nic,model=rtl8139,macaddr=2e:2e:2e:0:1:db,vlan=1 -net tap,ifname=rats2_1,vlan=1,script=no,downscript=no -net nic,model=rtl8139,macaddr=2e:2e:2e:0:2:db,vlan=2 -net tap,ifname=rats2_2,vlan=2,script=no,downscript=no -serial telnet:localhost:9108,server,nowait,nodelay -serial telnet:localhost:9208,server,nowait,nodelay -daemonize -pidfile /VMs/var/pids/rats2 -usbdevice tablet Command with explicit cache: aoss x86_64-softmmu/qemu-system-x86_64 -enable-kvm -name rats2 -drive file=/VMs/images/rats2.cow,if=ide,index=0,cache=writeback -m 650 -monitor telnet:localhost:9008,server,nowait,nodelay -vnc :8 -cdrom /VMs/cds/curodw.iso -boot dc -net nic,model=rtl8139,macaddr=2e:2e:2e:0:0:db,vlan=0 -net tap,ifname=rats2_0,vlan=0,script=no,downscript=no -net nic,model=rtl8139,macaddr=2e:2e:2e:0:1:db,vlan=1 -net tap,ifname=rats2_1,vlan=1,script=no,downscript=no -net nic,model=rtl8139,macaddr=2e:2e:2e:0:2:db,vlan=2 -net tap,ifname=rats2_2,vlan=2,script=no,downscript=no -serial telnet:localhost:9108,server,nowait,nodelay -serial telnet:localhost:9208,server,nowait,nodelay -daemonize -pidfile /VMs/var/pids/rats2 -usbdevice tablet Kernel modules: 2.6.32.2ish (gentoo-sources 2.6.32-gentoo-r1) configure: --audio-drv-list=alsa --kerneldir=/lib/modules/2.6.32-gentoo-r1/build CPU: Intel(R) Core(TM)2 Extreme CPU X9650 @ 3.00GHz (family 6, model 23, stepping 6, 6MB cache, 4 cores) ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=893831&aid=2926083&group_id=180599 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
