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Re: [PATCH 3/3] domaincapsmoc.c: mock virHostCPUGetMicrocodeVersion()



s/capsmoc.c/capsmock/

On a Monday in 2020, Daniel Henrique Barboza wrote:
Previous patch handled the runtime case where a non-x86 host is
fetching /proc/cpuinfo data for a microcode info that we know
it doesn't exist. This change alone speeded everything by a
bit for non-x86, but there is at least one major culprit left.

qemuxml2argvtest does several arch-specific tests, and a good
chunk of them are x86 exclusive. This means that 'hostArch'
will be seen as x86 for these tests, even when running in
non-x86 hosts. In a Power 9 server with 128 CPUs, qemuxmlargvtest

*qemuxml2argvtest

takes 298 seconds to complete in average, and 'perf record'
indicates that 95% of the time is spent in
virHostCPUGetMicrocodeVersion().


No surprise, we call it 23448 times.

This patch mocks virHostCPUGetMicrocodeVersion() to always return
0 in the tests, avoiding /proc/cpuinfo reads. This will make all
tests behave arch-agnostic, and the microcode value being 0 has no
impact on any existing test.

This is a CI speed across the board for all archs, including x86,
given that we're not reading /proc/cpuinfo in the tests. For
a Thinkpad T480 laptop with 8 Intel i7 CPUs, qemuxml2argvtest
went from 15.50 sec to 12.50 seconds. The performance gain is even
more noticeable for huge servers with lots of CPUs. For the
Power 9 server mentioned above, this patch speeds qemuxml2argvtest
to 9 seconds, down from 298 sec.


I assume the speedup for Power is measured for the whole series, not
just for this patch.

Signed-off-by: Daniel Henrique Barboza <danielhb413 gmail com>
---
src/util/virhostcpu.h  | 3 ++-
tests/domaincapsmock.c | 6 ++++++
2 files changed, 8 insertions(+), 1 deletion(-)


Reviewed-by: Ján Tomko <jtomko redhat com>

Jano

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