Re: [Xen-devel] [PATCH] turn off writable page tables

To:	"Andrew Theurer" <habanero@xxxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] turn off writable page tables
From:	"Jacob Gorm Hansen" <jacobg@xxxxxxx>
Date:	Tue, 25 Jul 2006 22:31:37 -0700
Cc:	Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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On 7/25/06, Andrew Theurer <habanero@xxxxxxxxxx> wrote:

Ian Pratt wrote:
>> on Xeon MP processor, uniprocessor dom0 kernel, pae=y:
>>
>> benchmark                c/s 10729 force_emulate
>> ------------------------ --------- -------------
>> lmbench fork+exit:       469.5833  470.3913   usec, lower is better
>> lmbench fork+execve:     1241.0000 1225.7778  usec, lower is better
>> lmbench fork+/sbin/bash: 12190.000 12119.000  usec, lower is better
>>
>
> It's kinda weird that these scores are so close -- I guess its just
> coincidence that we must be getting something like an average of 10-20
> pte's updated per pagetable page and the cost of doing multiple emulates
> perfectly balances the cost of unhooking/rehooking.


Just a silly question; is the old batched update mechanism totally out
of the picture here? Is it the cost of taking additional faults that
makes writable ptes as slow as emulation (which I suppose just means
shadow p.t.s)? Is there tension between shadow pt cache size inside
Xen and runtime performance?

Regards,
Jacob

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