[Qemu-devel] Qemu performance

[Qemu-devel] Qemu performance

[Lê Đức Tài]

[-- Attachment #1: Type: text/plain, Size: 317 bytes --]

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

[-- Attachment #2: Type: text/html, Size: 535 bytes --]

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]

[-- Attachment #1: Type: text/plain, Size: 1328 bytes --]

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

[-- Attachment #2: Type: text/html, Size: 2169 bytes --]

Re: [Qemu-devel] Về: Qemu performance

[Alexander Graf]

[-- Attachment #1: Type: text/plain, Size: 701 bytes --]


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

[-- Attachment #2: Type: text/html, Size: 1253 bytes --]