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Date: Tue, 11 Oct 2011 11:08:33 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] Hack integrating SeaBios / LinuxBoot option rom
 with QEMU trace backends
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To: Alexander Graf <agraf@suse.de>
Cc: Gleb Natapov <gleb@redhat.com>, seabios@seabios.org, qemu-devel <qemu-devel@nongnu.org>, "Richard W.M. Jones" <rjones@redhat.com>

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?

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