Re: [Qemu-devel] Hack integrating SeaBios / LinuxBoot option rom with QEMU trace backends

[Avi Kivity]

On 10/10/2011 09:01 PM, Alexander Graf wrote:
> >>  For example, one execution of QEMU produced the following log:
> >>
> >>    $ stap qemu-timing.stp
> >>    0.000 Start
> >>    0.036 Run
> >>    0.038 BIOS post
> >>    0.180 BIOS int 19
> >>    0.181 BIOS boot OS
> >>    0.181 LinuxBoot copy kernel
> >>    1.371 LinuxBoot copy initrd
> >
> >  Yeah, there was a thread a bit ago about the performance of the interface to 
> read the kernel/initrd.  I think at it was using single byte access instructions 
> and there were patches to use string accessors instead?  I can't remember where 
> that threaded ended up.
>
> IIRC we're already using string accessors, but are still slow. Richard had a 
> nice patch cooked up to basically have the fw_cfg interface be able to DMA its 
> data to the guest. I like the idea. Avi did not.
>
> And yes, bad -kernel performance does hurt in some workloads. A lot.

The rep/ins implementation is still slow, optimizing it can help.

What does 'perf top' say when running this workload?

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error compiling committee.c: too many arguments to function