Re: [Qemu-devel] win7 bad i/o performance, high insn_emulation and exists

[Gleb Natapov]

On Tue, Feb 21, 2012 at 12:16:16PM +0100, Peter Lieven wrote:
> On 21.02.2012 12:00, Gleb Natapov wrote:
> >On Tue, Feb 21, 2012 at 11:59:23AM +0100, Peter Lieven wrote:
> >>On 21.02.2012 11:56, Gleb Natapov wrote:
> >>>On Tue, Feb 21, 2012 at 11:50:47AM +0100, Peter Lieven wrote:
> >>>>>I hope it will make Windows use TSC instead, but you can't be sure
> >>>>>about anything with Windows :(
> >>>>Whatever it does now it eates more CPU has almost equal
> >>>>number of exits and throughput is about the same (15MB/s).
> >>>>If pmtimer is at 0xb008 it still reads it like hell.
> >>>>
> >>>>I checked with bcedit /v that useplatformclock is set to "No".
> >>>Yeah, today I noticed that it is likely virtio drivers that hammer
> >>>on PM timer (at least rip of the instruction that access it is
> >>>very close to rip of the instruction that access virtio pio).
> >>>Vadim, Windows driver developer,  is CCed.
> >>Ok, I will switch to IDE and e1000 to confirm this? Or does it not
> >>make sense?
> >>
> >It make perfect sense! Please try it.
> ~10MB/s. still a lot of 0xb008 reads.
> 
The same amount of reads essentially. So my theory is incorrect. Virtio
driver probably calls Windows function to do IO and the function
happens to be near the function that access PM timer.

I wonder why time stamps in your traces are so coarse-grained. What do
you see in /sys/bus/clocksource/devices/clocksource0/current_clocksource ?

--
                        Gleb.