[Xen-devel] Re: some performance issue of shadow2 on 2.6 Linux VMX and possible fix

[Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>]

Hi, 

At 17:13 +0800 on 23 Nov (1164301986), Yang, Xiaowei wrote:
> On ia32e system, old Linux 2.6 kernel (previous to 2.6.16) shares one l4
> page for all processes. At context switch, it replaces old L3 page in
> l4e with the new one. Current shadow discards old shadow page at the
> same time. When context switch (e.g. client/server model) is very
> frequent, it can be a high cost.
> 
> One solution is to pin L3 page as well as L4 page. It reserves previous
> process' L3 shadow page for later use. The test shows it benefits
> benchmark with frequent context switch such as OLTP (server/client),
> CPU2k (multi users) and specjbb (multi warehouses). 

Thanks!  Changeset 12533:2fd223c64fc6 pins l3 shadows, and falls back to
normal behaviour if we see the guest using too many l4 pages.

Cheers,

Tim.

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