Re: qemu-kvm-0.13.0 - winsows 2008 - chkdisk too slow

Avi Kivity
2011-01-06T13:26:49Z

On 01/06/2011 02:18 PM, Nikola Ciprich wrote:
> OK, got test environment running, but it seems to be running much faster
> there :(

Same host kernel?

> but as dan suggested, I can type monitor commands using virsh, so I can
> (carefully:)) continue debugging on this production machine..
> here's info registers:
> RAX=0000000000000007 RBX=00000000000000ac RCX=fffff880009d1015 RDX=00000000000003ce
> RSI=000000000000018a RDI=fffff8000163f737 RBP=0000000000000007 RSP=fffff88002588b08
> R8 =000000000000000f R9 =00000000000000ac R10=0000000000007b20 R11=0000000000000008
> R12=00000000000000a8 R13=0000000000000000 R14=000000000012c690 R15=00000000001d52d0
> RIP=fffff8000156ae48 RFL=00000202 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
>

That's cpu 0, which is busy writing stuff to the screen, not very
interesting.

> > Looks like vcpu 1 is spinning; perhaps that's normal. If you get hold
> > of the monitor, please disassemble around 0xfffff80001575d59.
> ouch, can You advice me on how do I do it? :-[

(qemu) cpu 1
(qemu) info registers
(qemu) x/100i 0xfffff80001575d59 - 35

> >
> > vcpu 0 is busy writing to vga (can you confirm)? looks like bank
> yes, seems like screen refreshing is quite slow, certainly in this rescue mode
> or what it is, it's not using any acceleration...

It's actually decelerated by synchronized_srcu_expedited(). It's one
area which got a large slowdown as the price for the great scalability
we achieved with srcu.

But wait, this doesn't make sense. If we see mmio to vga, then bank
switching is not involved, yet I see huge latencies on writes to vga io
ports.

Please install the qemu debuginfo package (if you built it yourself, I
hope it was with debug symbols enabled) and run 'perf top'.

> > switching is hitting synchronize_srcu_expedited(), which is known slow.
> > Unfortunately that only gets better in 2.6.38.
> >
> > You can try applying
> > http://git.kernel.org/?p=linux/kernel/git/sfr/linux-next.git;a=commit;h=46fdb0937f26124700fc9fc80da4776330cc00d3
> I'll be able to test this only on testing machine, or on this production maybe overnight..
> I'll prepare the kernel anyways..
>

I'm no longer sure this is the problem.

--
error compiling committee.c: too many arguments to function