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:

> 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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