Re: slow guest performance with build load, looking for ideas

[Erik Jacobson <erikj@sgi.com>]

>> Timing with the rotational stuff set to 1...
>>
>> real    14m13.015s
>> user    29m42.162s
>> sys     8m37.416s
>
> (user + sys) / real = 2.7
>
>> And finally, to confirm the numbers on the host with no guest running...
>> The same disk/filesystem, now mounted on the host instead of the guest, gave
>> this timing:
>>
>> real    6m13.398s
>> user    26m56.061s
>> sys     5m34.477s
>>    
>
> (user + sys) / real = 5.2
>
> I got 6.something in a guest!

> Please drop -usbdevice tablet and set the host I/O scheduler to  
> deadline.  Add cache=none to the -drive options.

yes, these changes make a difference.


Before starting qemu-kvm, I did this to change the IO scheduler:
BEFORE:
# for f in /sys/block/sd*/queue/scheduler; do cat $f; done
noop anticipatory deadline [cfq] 
noop anticipatory deadline [cfq] 

SET:
# for f in /sys/block/sd*/queue/scheduler; do echo "deadline" > $f; done

CONFIRM:
# for f in /sys/block/sd*/queue/scheduler; do cat $f; done
noop anticipatory [deadline] cfq 
noop anticipatory [deadline] cfq 


qemu command line.  Note that usbtablet is off and cache=none is used in
drive options:

/usr/bin/qemu-kvm -M pc -m 4096 -smp 8 -name f11-test -uuid b7b4b7e4-9c07-22aa-0c95-d5c8a24176c5 -monitor pty -pidfile /var/run/libvirt/qemu//f11-test.pid -drive file=/var/lib/libvirt/images/f11-test.img,if=virtio,index=0,boot=on,cache=none -drive file=/dev/sdb,if=virtio,index=1,cache=none -drive file=/var/lib/libvirt/images/test.img,if=virtio,index=2,cache=none -net nic,macaddr=54:52:00:46:48:0e,model=virtio -net user -serial pty -parallel none -usb -vnc cct201:1 -soundhw es1370 -redir tcp:5555::22


# rotation enabled this way in the guest, once the guest was started:
for f in /sys/block/vd*/queue/rotational; do echo 1 > $f; done

Test runs after make clean...
time (make -j12&&  make -j12 modules)

real	10m25.585s
user	26m36.450s
sys	8m14.776s

2nd trial (make clean followed by the same test again.
real	9m21.626s
user	26m42.144s
sys	8m14.532s