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recompile QEMU for raspberry 2 to use 4 cores

Posted: Mon Feb 09, 2015 10:52 am
by GiorgioFoX
Hello,
I've installed Windows XP on raspberry 2 using QEMU.

The emulation is very slow, but qemu use only one core of raspberry 2, so the overall cpu level is about 25%

How let QEMU use 100% ?
I thinks that I need to recompile QEMU... what option I need to use?

Thanks in advance
Giorgio

Re: recompile QEMU for raspberry 2 to use 4 cores

Posted: Mon Feb 09, 2015 6:49 pm
by Mequa
QEMU is emulating a single-core x86 CPU. AFAIK, this emulation cannot run parallel on all 4 ARM cores, so can only use one core. Emulating a single-core CPU using parallel cores is VERY non-trivial to implement.

Windows XP is going to be way too slow, the minimum requirements are along the lines of a 300MHz Intel CPU. The Pi 2 can only emulate an Intel CPU a small fraction of this speed. It may be worth sticking with MS-DOS and Windows 3.11, and perhaps Windows 95.

Re: recompile QEMU for raspberry 2 to use 4 cores

Posted: Fri Feb 20, 2015 10:43 am
by cia48621793
one core of Core i3 of any version already beat the CPU of Pi 2.

Re: recompile QEMU for raspberry 2 to use 4 cores

Posted: Fri Feb 20, 2015 11:28 am
by mikerr
cia48621793 wrote:one core of Core i3 of any version already beat the CPU of Pi 2.
Silly comment; but to respond - Cost, size and power requirements ? ;)

Re: recompile QEMU for raspberry 2 to use 4 cores

Posted: Sat Feb 21, 2015 1:31 am
by cia48621793
mikerr wrote:
cia48621793 wrote:one core of Core i3 of any version already beat the CPU of Pi 2.
Silly comment; but to respond - Cost, size and power requirements ? ;)
The closet Intel CPU for Pi 2's is N270 my guess, N270 runs Linux and Hackintosh(yup) quiet well, but I have to wait for 30 seconds to boot up the Windows, even if I'm using XP.

Re: recompile QEMU for raspberry 2 to use 4 cores

Posted: Sat Feb 21, 2015 4:40 am
by Mequa
cia48621793 wrote:
mikerr wrote:
cia48621793 wrote:one core of Core i3 of any version already beat the CPU of Pi 2.
Silly comment; but to respond - Cost, size and power requirements ? ;)
The closet Intel CPU for Pi 2's is N270 my guess, N270 runs Linux and Hackintosh(yup) quiet well, but I have to wait for 30 seconds to boot up the Windows, even if I'm using XP.
N270 is a single-core 1.6GHz Intel Atom CPU used in old netbooks (I used to have 2 which have since died), Pi 2's CPU is a quad-core 900MHz (1GHz overclocked) ARM Cortex-A7. I'm quite sure the clock speeds do not directly compare but the ARM Cortex-A7 is slower per MHz than the N270.

Performance-wise they are quite close for general purpose use, thanks to the quad core ARM, but when it comes to emulation, single-core performance is what counts, so the Pi 2 would most likely be considerably slower for that purpose than an old Atom netbook. Emulating x86 too is necessary on the Pi 2's ARM but not on the N270, which is native x86, so while a N270 can run Windows XP well, a Cortex-A7 can NOT.

Re: recompile QEMU for raspberry 2 to use 4 cores

Posted: Sat Feb 21, 2015 5:08 pm
by cia48621793
Mequa wrote: Performance-wise they are quite close for general purpose use, thanks to the quad core ARM, but when it comes to emulation, single-core performance is what counts, so the Pi 2 would most likely be considerably slower for that purpose than an old Atom netbook. Emulating x86 too is necessary on the Pi 2's ARM but not on the N270, which is native x86, so while a N270 can run Windows XP well, a Cortex-A7 can NOT.
Yes, I should haven't compared x86 and ARM, they have different architecture design, sorry for being such misdirection.

Re: recompile QEMU for raspberry 2 to use 4 cores

Posted: Mon Apr 20, 2015 5:50 pm
by sdecesari
GiorgioFoX wrote:Hello,
I've installed Windows XP on raspberry 2 using QEMU.

The emulation is very slow, but qemu use only one core of raspberry 2, so the overall cpu level is about 25%

How let QEMU use 100% ?
I thinks that I need to recompile QEMU... what option I need to use?

Thanks in advance
Giorgio
I'm trying to do the same. But i've yet to been able to install windows xp (but i have activated the HYP virtualization function on the Raspberry Pi2.

Could you tell exactly which steps you did in order to run Xp on qemu?

Thanks.

Stefano