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:

>Hi Anthony:
>	I think you made misunderstanding to this patch. Current Qemu in
>Xen is already DMA enabled. If I remembered correctly, it happens since
>we change DM from Bochs to Qemu.
>	Without this patch, guest IO operation that trigger DMA (like
>port 0xc000 write) will wait in Qemu till the DMA operation is
>completed, that is original single thread IDE device model mean. 
>	With this patch, a seperate thread will service the dma
>operation started by IO operation, and interrupt target processor when
>it is completed, while the main thread can rapidly return to guest (like
>0xc000 write).
>  
>
Yup, the site I linked to has two patches: a DMA patch and a concurrent 
IO patch.

Here's a direct link: 
http://people.brandeis.edu/~jcoiner/qemu_idedma/qemu_concurrent_io.patch

It's using the same basic approach as your patch (another thread waits 
for completion of IO event).  I'm pointing it out though in case there's 
a desire to stay closer to QEMU upstream when possible.  Might enable 
more code sharing in the future.

Regards,

Anthony Liguori

>Thanks,eddie
>
>Anthony Liguori wrote:
>  
>
>>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
>>
>>    
>>
>
>  
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