[dm-devel] Thoughts on removing the remap cache

[Dan Smith]

Hi Fujita,

I've been very pleased with the removal of the remap caching from
dm-userspace because performance seems to be good and complexity is
lower.

However, all of my tests up until now have been with dbench.  I think
that dbench works well in cases where latency is high, which is of
course the case since we're sending all requests to userspace.  When I
try to boot a Xen domU with root on dm-userspace (without the
caching), it is *painfully* slow.  I assume this is because the domU
boot is doing a lot of synchronous, sequential operations.

Since domU performance was good when I was caching mappings in the
kernel, I would assume that the difference in performance is related
to the caching.

What do you think?

-- 
Dan Smith
IBM Linux Technology Center
Open Hypervisor Team
email: danms at us.ibm.com
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