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McKenney" , "Frederic Weisbecker" , "Neeraj Upadhyay" , "Joel Fernandes" , "Josh Triplett" , "Boqun Feng" , "Uladzislau Rezki" , "Mathieu Desnoyers" , "Lai Jiangshan" , "Zqiang" , "Pedro Falcato" , "Suren Baghdasaryan" Cc: , , , , Subject: Re: [PATCH for-next v3 1/9] slub_kunit: fall back to SW perf events when HW PMU is not available From: "Alexei Starovoitov" X-Mailer: aerc References: <20260615-kfree_rcu_nolock-v3-0-70a54f3775bb@kernel.org> <20260615-kfree_rcu_nolock-v3-1-70a54f3775bb@kernel.org> In-Reply-To: <20260615-kfree_rcu_nolock-v3-1-70a54f3775bb@kernel.org> On Mon Jun 15, 2026 at 4:05 AM PDT, Harry Yoo (Oracle) wrote: > slub_kunit uses hardware perf events to invoke _nolock() APIs from NMI > context. However, creating a HW perf event fails when there is no > hardware PMU, or when running in a virtualized environment without a > virtual PMU configured. > > Since tests are often performed in virtualized environments, fall back > to a SW perf event so that the test can still run, even if it cannot > cover IRQ-disabled sections. Frankly, I wouldn't bother with this fallback, since it completely misses irq disabled section which is the one to test with *_nolock(). VMs need to configured properly. Even nested VMs support PERF_COUNT_HW_CPU_CYCLES. Also in overflow_handler_test_nolock() I would add even->hw.interrupts =3D 0; to the end to make sure it actually stress tests things. Without it NMIs are not firing quickly enough.