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

[Daniel Henrique Barboza]

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

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.

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

diff --git a/src/util/virhostcpu.h b/src/util/virhostcpu.h
index 11cbcd72a3..6148f9e66f 100644
--- a/src/util/virhostcpu.h
+++ b/src/util/virhostcpu.h
@@ -75,7 +75,8 @@ virBitmapPtr virHostCPUGetSiblingsList(unsigned int cpu);
 
 int virHostCPUGetOnline(unsigned int cpu, bool *online);
 
-unsigned int virHostCPUGetMicrocodeVersion(virArch hostArch);
+unsigned int
+virHostCPUGetMicrocodeVersion(virArch hostArch) G_GNUC_NO_INLINE;
 
 int virHostCPUGetMSR(unsigned long index,
                      uint64_t *msr);
diff --git a/tests/domaincapsmock.c b/tests/domaincapsmock.c
index 90e17c19f0..d81a898dc0 100644
--- a/tests/domaincapsmock.c
+++ b/tests/domaincapsmock.c
@@ -34,3 +34,9 @@ virHostCPUGetKVMMaxVCPUs(void)
 {
     return INT_MAX;
 }
+
+unsigned int
+virHostCPUGetMicrocodeVersion(virArch hostArch G_GNUC_UNUSED)
+{
+    return 0;
+}
-- 
2.26.2