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

["Yang, Xiaowei" <xiaowei.yang@xxxxxxxxx>]

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). 

But it also introduces some overhead. As L3 page table is pinned, it
needs 1+ extra page fault to be unpinned after the process is
terminated. KB's performance has some impact. 

Thanks, 
Xiaowei

Attachment: sh2.patch
Description: sh2.patch

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