RE: [Xen-ia64-devel] [PATCH] unify vtlb and vhpt

[Kouya Shimura <kouya@xxxxxxxxxxxxxx>]

Dong, Eddie writes:
> This can be simply solved by increasing vTLB size, or 
> use same memory with VHPT.

The problem is, how much size is suitable?
There is a trade off. The larger size consumes a time for ptc.e
emulation and causes a serious slowdown for a Windows guest.

Currently vTLB size is configurable but ordinary users
can't understand what vTLB is.
A purpose of this patch is to make users free from
setting vTLB size.

> If compare sharing vTLB/VHPT memory with putting vTLB 
> in VHPT, I voke for former one since they are using totally
> different hash/tag algorithm,save low level VHPT walk
>  time and more simple (we need to avoid those vTLB entries
> to be in the head of VHPT table, otherwise performance lost).

I agree that my patch makes it complex. But I think it hardly
increases VHPT walk time. Because there is no difference between
collision of VHPT and collision of VTLB.

To tell the truth, I rewrote the vtlb_thash() function before.
See.
http://lists.xensource.com/archives/html/xen-ia64-devel/2007-08/msg00108.html

I think the algorithm is the same as HW. 
I did a reverse engineering on a Montecito processor.
(I'm afraid Montvale use the different algorithm...)

Thanks,
Kouya

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