From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.fraser@eu.citrix.com>
Subject: Re: Root cause of the issue that HVM guest boots slowly
	with pvops dom0
Date: Thu, 21 Jan 2010 08:44:33 +0000
Message-ID: <C77DC471.6ED6%keir.fraser@eu.citrix.com>
References: <4B580D6A.4030802@intel.com>
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To: "Yang, Xiaowei" <xiaowei.yang@intel.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
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On 21/01/2010 08:16, "Yang, Xiaowei" <xiaowei.yang@intel.com> wrote:

> - Limiting vCPU# of dom0 is always an easiest one - you may call it workaround
> rather than a solution:) It not only reduces the total # of resched IPI ( =
> mlock# * (vCPU#-1)), but reduces the cost of each handler - because of
> spinlock. 
> But the impact is still there, more or less, when vCPU# > 1.
> 
> - To remove mlock, another sharing method is needed between dom0 user space
> app
> and Xen HV.

A pre-mlock()ed memory page for small (sub-page) hypercalls? Protected with
a semaphore: failure to acquire semaphore means take slow path. Have all
hypercallers in libxc launder their data buffers through a new interface
that tries to grab and copy into the pre-allocated buffer.

 -- Keir