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Re: [PATCH] target/riscv: Use a direct cast for better performance
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From: |
Richard W.M. Jones |
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Subject: |
Re: [PATCH] target/riscv: Use a direct cast for better performance |
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Date: |
Sat, 7 Oct 2023 10:10:03 +0100 |
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User-agent: |
Mutt/1.5.21 (2010-09-15) |
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
Read my programming and virtualization blog: http://rwmj.wordpress.com
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