Re: kvm very slow

Dor Laor
2007-08-07T07:44:43Z

>no ideas what can be done? why it is so slow?

Let's try to catch the cause for the 74k ioexits per second.
Please add #define DEBUG_IOPORT in qemu/vl.c and qemu/exec.c and
recompile.
After that when the guest runs and does 74k ioexits on idle, enter the
qemu's monitor (ctrl-alt-1)
enter 'log ioport'. All guest's ioport access will be written to
/tmp/qemu.log.
Be kind enough to calculate the statistics of ioport access per port
number a second.
With the numbers we can see the hardware that causes the slowness.
-- Dor.

btw: are you using kvm-33 or older?

>
>i've tried the "-L /usr/shar/kvm" to use the kvm-bios but no better
>performance ...
>
>Am Donnerstag, den 02.08.2007, 11:24 +0300 schrieb Avi Kivity:
>> Ulrich Schreiner wrote:
>> > dmesg|grep kvm
>> >
>> > SELinux: initialized (dev kvmfs, type kvmfs), uses genfs_contexts
>> > kvm: emulating exchange as write
>> >
>> >
>>
>> There may be messages that aren't prefixed with 'kvm:' (that's a bug
>> btw). Please check.
>>
>> > now booting into a F7 image, after the system is ready (and in
>idle):
>> >
>> > top
>> > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+
>COMMAND
>> > 14917 root 20 0 332m 71m 66m S 6 0.9 1:17.05 qemu-
>kvm
>> > 14954 root 20 0 14552 1072 812 R 0 0.0 0:00.01 top
>> > 1 root 20 0 10320 680 572 S 0 0.0 0:02.02 init
>> >
>> > kvm_stat (snapshot):
>> >
>> > kvm statistics
>> >
>> > exits 12254399 79079
>> > halt_exits 326543 4632
>> > invlpg 0 0
>> > io_exits 6539798 74320
>> > irq_exits 43523 29
>> > irq_window 4984 0
>> > mmio_exits 1319016 0
>> > pf_fixed 3140955 56
>> > pf_guest 448187 6
>> > request_irq 0 0
>> > signal_exit 39728 0
>> > tlb_flush 29511 31
>> >
>>
>> Wow -- lots of I/O exits. What does 'top' in the guest say? 'hdparm
>> /dev/hda' in the guest?
>>
>> > when logging into the virtual machine (via ssh) the virtual world
is
>> > very slow: i set the time with "ntpdate" and wait exact one minute
>in
>> > reality. in the virtual image only 24sec are gone!
>> >
>> > and everything else in the image is really slow.
>> >
>> >
>>
>
>
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