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

  • To: Xen development list <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Andrew Theurer <habanero@xxxxxxxxxx>
  • Date: Mon, 05 Jun 2006 16:45:50 -0500
  • Delivery-date: Mon, 05 Jun 2006 14:46:50 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

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()?


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