Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do to speedup the emulation?

[Dennis Luehring]

Am 30.07.2015 um 09:52 schrieb Aurelien Jarno:
> On 2015-07-30 05:52, Dennis Luehring wrote:
> > Am 29.07.2015 um 17:01 schrieb Aurelien Jarno:
> > >The point is that emulation has a cost, and it's quite difficult to
> > >to lower it and thus improve the emulation speed.
> >
> > so its just not strange for you to see an 1/100...200 of the native x64
> > speed under qemu/SPARC64
> > i hoped that someone will jump up an shout "its impossible - it needs to be
> > a bug" ...sadly not
>
> Overall the ratio is more around 10, but in some specific cases where
> the TB cache is inefficient and TB can't be linked or with an
> inefficient MMU, a ratio of 100 is possible.


sysbench (0.4.12) --num-threads=1 --test=cpu --cpu-max-prime=2000 run
   Host x64    :   1.3580s
   Qemu SPARC64: 184.2532s

sysbench shows nearly ration of 200

> Also remember you are comparing apples and oranges there. A GCC compiler
> for x86-64 and for SPARC64 can't really be compared, even if the
> front-end and middle-end part are the same. The job of generating the
> assembly code is not the same and might take more or less time depending
> on the architecture complexity.

that is true - but its slow even when i compile non-complex stuff, no 
headers, simple integer math
i try to come up with an good example

> Finally make sure you have enough RAM in your guest and that GCC isn't
> swapped. Recent GCC versions needs a lot of memory and the default 128MB
> might not be enough.

during all my test 70-80% free RAM, no swapping ever