[Xen-devel] Why is 'emulate' as good as writable PT's?

[Andrew Theurer <habanero@xxxxxxxxxx>]

We have been doing some scalability work, and we noticed that forcing 
'emulate' in arch.x86/mm.c achieves the same performance on 1-way dom0.  
For example:
xen-unstable, changeset 10200, i386 with PAE, 1-way

benchmark       xen0   xen0+emulate
-------------   ----   ----
reaim_fserver   4421   4426
reaim_compute   2555   2531
SDET            4759   4810

The reaim benchmarks probably don't have much fork(), where I'd expect 
writable page tables to help, but SDET has a ton of fork+exec.
Could there be situations were we are inadvertently triggering a 
writable page table, where we should just be doing a update_va_mapping()?
-Andrew


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