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

[Anthony Liguori <aliguori@us.ibm.com>]

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@intel.com>
>>Signed-off-by: Xiaowei Yang <xiaowei.yang@intel.com>
>>
>>-Xiaowei
>>    
>>
>
>
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