[Qemu-devel] threads on qemu

[Qemu-devel] threads on qemu

[C.W. Betts]

I was thinking, maybe qemu could use threads for at least every processor it 
emulates (on emulated smp computers) and, at the most, every single device 
emulated.  This would help users who have multiple cores, but it might 
impact performance on those of us who don't.

Just an idea I'm throwing out. 

Re: [Qemu-devel] threads on qemu

[Paul Brook]

On Monday 21 January 2008, C.W. Betts wrote:
> I was thinking, maybe qemu could use threads for at least every processor
> it emulates (on emulated smp computers) and, at the most, every single
> device emulated.  This would help users who have multiple cores, but it
> might impact performance on those of us who don't.

Please read previous discussions on this mailing list.

I'd be surprised if putting device emulation  in a separate thread makes much 
difference. The really slow bits (waiting for IO to complete) are already 
asynchronous. Most other device accesses are very short, so you'd waste more 
time through synchronisation than you gain from putting them is a separate 
thread.

Splitting multiple CPUs into multiple threads is extremely hard to get right, 
especially when your host system provides less strict ordering and atomicity 
guarantees than those required by the guest system.

Paul

Re: [Qemu-devel] threads on qemu

[Johannes Schindelin]

Hi,

On Mon, 21 Jan 2008, C.W. Betts wrote:

> I was thinking, maybe qemu could use threads for at least every 
> processor it emulates (on emulated smp computers) and, at the most, 
> every single device emulated.  This would help users who have multiple 
> cores, but it might impact performance on those of us who don't.

This is an idea that comes up every once in a while:

http://lists.gnu.org/archive/html/qemu-devel/2007-07/msg00369.html

Ciao,
Dscho

Re: [Qemu-devel] threads on qemu

[C.W. Betts]

Still, is there a way to make qemu take advantage of multiple cores?  They 
are pretty commonplace in new computers (is there any selling computer that 
doesn't have multiple cores?).
----- Original Message ----- 
From: "Johannes Schindelin" <Johannes.Schindelin@gmx.de>
To: "C.W. Betts" <computers57@hotmail.com>
Cc: <qemu-devel@nongnu.org>
Sent: Monday, January 21, 2008 9:10 AM
Subject: Re: [Qemu-devel] threads on qemu


> Hi,
>
> On Mon, 21 Jan 2008, C.W. Betts wrote:
>
>> I was thinking, maybe qemu could use threads for at least every
>> processor it emulates (on emulated smp computers) and, at the most,
>> every single device emulated.  This would help users who have multiple
>> cores, but it might impact performance on those of us who don't.
>
> This is an idea that comes up every once in a while:
>
> http://lists.gnu.org/archive/html/qemu-devel/2007-07/msg00369.html
>
> Ciao,
> Dscho
>
>
>
> 

Re: [Qemu-devel] threads on qemu

[Daniel P. Berrange]

On Mon, Jan 21, 2008 at 09:57:54AM -0700, C.W. Betts wrote:
> Still, is there a way to make qemu take advantage of multiple cores?  They 
> are pretty commonplace in new computers (is there any selling computer that 
> doesn't have multiple cores?).

If you've got recent x86 CPUs, then they may well have hardware virtualization
support, in which case you can use KVM which can take advantage of multiple
cores. At least for native host/guest i686 & x86_64 combos.

Dan.
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