Re: [PATCH] target/riscv: Use a direct cast for better performance

["Richard W.M. Jones" <rjones@redhat.com>]

If you're interested in how I found this problem, it was done using
'perf report -a -g' & flamegraphs.  This is the flamegraph of qemu (on
the host) when the guest is running the parallel compile:

  http://oirase.annexia.org/tmp/qemu-riscv.svg

If you click into 'CPU_0/TCG' at the bottom left (all the vCPUs
basically act alike), and then go to 'cpu_get_tb_cpu_state' you can
see the call to 'object_dynamic_cast_assert' taking considerable time.

If you zoom out, hit Ctrl F and type 'object_dynamic_cast_assert' into
the search box then the flamegraph will tell you this call takes about
6.6% of total time (not all, but most, attributable to the call from
'cpu_get_tb_cpu_state' -> 'object_dynamic_cast_assert').

There are several other issues in the flamegraph which I'm trying to
address, but this was the simplest one.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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