Re: [Xen-devel][PATCH][VT] Multithread IDE device model ( was: RE: [Xen-devel] [PATCH]Make IDE dma tranfer run in another thread inqemu)

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Dong, Eddie wrote:

> Keir:
>         This is to to make the IDE device model multithreading so that
> the VMX domain IO access completion (triggering DMA operation) can be
> asynchronize with the completion of DMA operation. With this patch we
> get 8%--14% performance gain for kernel build.
> 	Thanks, 
> eddie
>  
Hi Eddie,

There was a patch floating around on qemu-devel recently to make IDE DMA 
concurrent.  Fabrice is planning to include it in QEMU as long as there 
are no regressions.  It may already be in CVS.
See http://people.brandeis.edu/~jcoiner/qemu_idedma/qemu_dma_patch.html

The reported performance improvement IO is up to 20% so it's definitely 
worth applying...
Regards,

Anthony Liguori

> Yang, Xiaowei wrote:
>  
>
> > Originally in qemu when a IDE dma transfer is started which is
> > triggered by access to 0xc000 port in VMX, qemu will blocked there
> > until it finished. And during that block, there are extra dom
> > switches between dom0 and idle domain, and VMX can't be resumed. By
> > making real IDE dma tranfer run in another thread, qemu will return
> > and VMX resume on time and there are fewer cycle wasted.
> >
> > Signed-off-by: Ke Yu <ke.yu@xxxxxxxxx>
> > Signed-off-by: Xiaowei Yang <xiaowei.yang@xxxxxxxxx>
> >
> > -Xiaowei
> >    
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>  
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