linux-kernel - [PATCH 0/1] KVM: selftests: pmu_counters_test: increase robustness of LLC cache misses

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Message-Id: <20240621204305.1730677-1-mlevitsk@redhat.com>
Date: Fri, 21 Jun 2024 16:43:04 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>,
	linux-kselftest@...r.kernel.org,
	Shuah Khan <shuah@...nel.org>,
	linux-kernel@...r.kernel.org,
	Sean Christopherson <seanjc@...gle.com>,
	Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 0/1] KVM: selftests: pmu_counters_test: increase robustness of LLC cache misses

Recent CI failures brought my attention to the fact that pmu_counters_test
sometimes fails because it doesn't get any LLC cache misses.

It apparently happens because CLFLUSH can race with CPU prediction.

To attempt to fix this, implement a more aggressive cache flushing - now it is flushed
on each iteration of the measured loop which should at least reduce by order
of magnitude the chance of this happening.

This patch survived more that a day of running in a loop on a Comet Lake machine,
where the test used to fail after about 10-20 minites.

Best regards,
	Maxim Levitsky

Maxim Levitsky (1):
  KVM: selftests: pmu_counters_test: increase robustness of LLC cache
    misses

 .../selftests/kvm/x86_64/pmu_counters_test.c  | 20 +++++++++----------
 1 file changed, 9 insertions(+), 11 deletions(-)

-- 
2.26.3