[Qemu-devel] Qemu performance

[Qemu-devel] Qemu performance

[Lê Đức Tài]

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Hi,
I have a question about performance of Qemu for powerpc.
When I'm changing the CPU clock for taihu board from 33Mhz to 330Mhz by setting 
the PLL value, the performance of Guest OS is not increased. I use nbench to 
measure the guest performance.
Is qemu always running as maximum performance?

Thank.
Tai

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Re: [Qemu-devel] Qemu performance

[Mulyadi Santosa]

Hi... :)

2011/6/29 Lê Đức Tài <letai_dhqg@yahoo.com.vn>:
> Hi,
> I have a question about performance of Qemu for powerpc.
> When I'm changing the CPU clock for taihu board from 33Mhz to 330Mhz by
> setting the PLL value, the performance of Guest OS is not increased. I use
> nbench to measure the guest performance.
> Is qemu always running as maximum performance?
Yes...

Logically, nbench is just pressing out all of your processor can do
(CPU bound tasks). In this case, emulated guest processor clock has
very little meaning IMO. After all, AFAIK it's just a complimentary
info so it is seen as "real processor".


-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

[Qemu-devel] Về: Qemu performance

[Lê Đức Tài]

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Thank for your answer.
Beside nbench, I'm also using Dhrystone to measure the guest cpu performance. 
The performance does not much diffetence too.
Is the emulated guest performance not depend on guest processor clock?

Tai




________________________________
Từ: Mulyadi Santosa <mulyadi.santosa@gmail.com>
Đến: Lê Đức Tài <letai_dhqg@yahoo.com.vn>
Cc: "qemu-devel@nongnu.orgDevelopers" <qemu-devel@nongnu.org>
Gửi ngày: 17:27:20, Thứ Tư, 29 tháng 6 2011 
Chủ đề: Re: [Qemu-devel] Qemu performance

Hi... :)

2011/6/29 Lê Đức Tài <letai_dhqg@yahoo.com.vn>:
> Hi,
> I have a question about performance of Qemu for powerpc.
> When I'm changing the CPU clock for taihu board from 33Mhz to 330Mhz by
> setting the PLL value, the performance of Guest OS is not increased. I use
> nbench to measure the guest performance.
> Is qemu always running as maximum performance?
Yes...

Logically, nbench is just pressing out all of your processor can do
(CPU bound tasks). In this case, emulated guest processor clock has
very little meaning IMO. After all, AFAIK it's just a complimentary
info so it is seen as "real processor".


-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

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Re: [Qemu-devel] Về: Qemu performance

[Alexander Graf]

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On 30.06.2011, at 04:11, Lê Đức Tài <letai_dhqg@yahoo.com.vn> wrote:

> Thank for your answer.
> Beside nbench, I'm also using Dhrystone to measure the guest cpu performance. 
> The performance does not much diffetence too.
> Is the emulated guest performance not depend on guest processor clock?
> 

Please don't top-post.

Qemu doesn't emulate cycle-accurately. Instead, it converts guest code to host code and executes it as fast as it can. So whatever you tell the guest on the cpu speed doesn't really matter. Except for the timebase of course :).

Mind if I ask what exactly you're trying to do with ppc emulation? I'm interested in use cases people have.


Alex

> Tai

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Re: [Qemu-devel] Qemu performance

[Lê Đức Tài]

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On 08.07.2011, at 16:55, Alexander Graf <agraf@suse.de> wrote:


> I see. Qemu always gives you "best performance", as it can't throttle the guest 
>:). Btw, I'd be happy to merge your custom board (or at least some components of 
>it if they are reasonably mainstream) upstream, if you think it makes sense and 
>the code is in good shape.
>
> Alex

I'm a new in Qemu.
I'm beginning to develop my custom board, and the is no components is 
implemented :).
So, I'm looking forward to get help from you.

Thank you for your support from the past till now.

Tai

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Re: [Qemu-devel] Qemu performance

[Alexander Graf]

On 08.07.2011, at 04:55, Lê Đức Tài wrote:

> On 30.06.2011, at 15:24, Alexander Graf <agraf@suse.de> wrote:
> 
> >  On 30.06.2011, at 04:11, Lê Đức Tài <letai_dhqg@yahoo.com.vn> wrote:
> >
> >  > Thank for your answer.
> >  > Beside nbench, I'm also using Dhrystone to measure the guest cpu performance. 
> >  > The performance does not much diffetence too.
> >  > Is the emulated guest performance not depend on guest processor clock?
> >
> >  Please don't top-post.
> >
> >  Qemu doesn't emulate cycle-accurately. Instead, it converts guest code to host code and executes it as fast as it can. So whatever you tell the >  guest on the cpu speed doesn't really matter. Except for the timebase of course :).
> >
> >  Mind if I ask what exactly you're trying to do with ppc emulation? I'm interested in use cases people have.
> >
> >  Alex
> 
> Thank you, 
> Exactly I want to emulate my ppc custom board (ppc440) with many features supporting as Ethernet, HDD, VGA, .. for my test environment (I have a software that running on ppc440).
> And I wan to get the best performance of Qemu.

I see. Qemu always gives you "best performance", as it can't throttle the guest :). Btw, I'd be happy to merge your custom board (or at least some components of it if they are reasonably mainstream) upstream, if you think it makes sense and the code is in good shape.


Alex

Re: [Qemu-devel] Qemu performance

[Lê Đức Tài]

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On 30.06.2011, at 15:24, Alexander Graf <agraf@suse.de> wrote:


>  On 30.06.2011, at 04:11, Lê Đức Tài <letai_dhqg@yahoo.com.vn>  wrote:
>

>  > Thank for your answer.
>  > Beside nbench, I'm also  using Dhrystone to measure the guest cpu 
>performance. 
>
>  > The performance does not much diffetence too.
>  > Is the emulated guest performance not depend on guest processor clock?
>

>  Please don't top-post.
>

>  Qemu doesn't emulate cycle-accurately. Instead, it converts guest code to host 
>code and executes it as fast as it can. So whatever you tell the >  guest on the 
>cpu speed doesn't really matter. Except for the timebase of course :).
>

>  Mind if I ask what exactly you're trying to do with ppc emulation? I'm 
>interested in use cases people have.
>

>  Alex
Thank you, 
Exactly  I want to emulate my ppc custom board (ppc440) with many features 
supporting as Ethernet, HDD, VGA, .. for my test environment (I have a software 
that  running on ppc440).
And I wan to get the best performance of Qemu.

Tai

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