On 03/20/10 04:10, Tim Judd wrote:
This is the first time I've heard of any penalty on HVM systems. What
I'd like to know, given that I now have some googl'ing I need to do
about this, is that for those who have already done this; how big is
the impact? Is it so much that general usability and patience a
sysadmin does not normally have would drive them insane?
Nobody's measuring it, to my knowledge, because nobody's had to -- if
it's 'good enough' for them, they'll stick with what's there.
Of course, blue chip quality engineering is normally what I pitch for in
the beginning. Then, we identify what the client can actually get away with.
This is largely borne out of experience subcontracting for companies in
the 3GPP space here in the UK, and it does require excellent
communication between client and consultant. Any pitch to mass consumer
market, usually requires the same level of engineering and project
management expertise, as for a blue chip b2b sale.
There is a performance penalty, because Xen has to emulate real hardware
for HVM, using code largely cribbed from QEMU.
Normally this happens within the hypervisor itself, however, this is
problematic, because there is then no good way to book the CPU/memory/IO
involved to the domU doing the I/O. This in turn affects scheduling
Using the grant_table abstraction, though, it's possible to shuffle it
into a 'driver domain', as I/O's to the 'driver domain' (another stub
Xen domain which hosts the drivers) can then still benefit from
grant_table's page flipping in shared memory, whilst booking the I/O so
we have a reflection of the true cost of running that HVM domU.
I strongly feel pv_ops is the right way to go, however this innovation
is happening outside of Citrix itself; it's mostly the Fedora camp who
are pushing it.
You could consider it a Xen fork. No one is doing this work 'for free',
the cost of the innovation is borne by their employers in their line of
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