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Re: [Xen-ia64-devel] [PATCH 0/2][RFC] set rr0 to rr4 hyperprivop

from [Alex Williamson]

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To:	Isaku Yamahata <yamahata@xxxxxxxxxxxxx>
Subject:	Re: [Xen-ia64-devel] [PATCH 0/2][RFC] set rr0 to rr4 hyperprivop
From:	Alex Williamson <alex.williamson@xxxxxx>
Date:	Tue, 31 Jul 2007 09:41:10 -0600
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On Mon, 2007-07-30 at 14:59 +0900, Isaku Yamahata wrote:
> This patch introduce set rr0 to rr4 hyperprivop to reduce context switch
> overhead.
> 
> Linux/ia64 changes region registers from rr0 to rr4 when context switch
> so that XenLinux issues 5 set_rr hyperprivops.
> This patch introduces the hyperprivops to change and reduce the cost
> to about 1/4 - 1/5. This rage is very reasonable because its overhead
> comes from hypercall trap cost.
> 
> [PATCH 1/2][RFC] set rr0 to rr4 hyperprivop: Xen side
> [PATCH 2/2][RFC] set rr0 to rr4 hyperprivop: Linux side

Hi Isaku,

   I haven't been able to measure a performance difference from this,
but is there any reason not to do it?  It looks like a standard
hypercall batching technique and the paravirtualization impact to the
guest is quite low.  Thanks,

        Alex

-- 
Alex Williamson                             HP Open Source & Linux Org.


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