Anthony Liguori wrote:
[...]
FWIW, the l1_phys_map table is a current hurdle in getting performance.
When we use proper accessors to access the virtio_ring, we end up taking
a significant performance hit (around 20% on iperf). I have some simple
patches that implement a page_desc cache that cache the RAM regions in a
linear array. That helps get most of it back.
I'd really like to remove the l1_phys_map entirely and replace it with a
sorted list of regions. I think this would have an overall performance
improvement since its much more cache friendly. One thing keeping this
from happening is the fact that the data structure is passed up to the
kernel for kqemu. Eliminating that dependency would be a very good thing!
If the l1_phys_map is a performance bottleneck it means that the
internals of QEMU are not properly used. In QEMU/kqemu, it is not
accessed to do I/Os : a cache is used thru tlb_table[]. I don't see why
KVM cannot use a similar system.