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[91.219.240.17]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82f8ec23b19sm22580923b3a.59.2026.04.23.00.50.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Apr 2026 00:50:26 -0700 (PDT) From: Vitaly Kuznetsov To: Piotr Zarycki Cc: kvm@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, shuah@kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, Piotr Zarycki Subject: Re: [PATCH v2] KVM: selftests: hyperv_tlb_flush: replace NOP loop with udelay() In-Reply-To: <20260422130307.1171808-1-piotr.zarycki@gmail.com> References: <87v7djgoji.fsf@redhat.com> <20260422130307.1171808-1-piotr.zarycki@gmail.com> Date: Thu, 23 Apr 2026 09:50:16 +0200 Message-ID: <87se8mglon.fsf@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Piotr Zarycki writes: > Replace the open-coded NOP loop with udelay() which was added to KVM > selftests in commit 6b878cbb87bf ("KVM: selftests: Add guest udelay() > utility for x86"). The NOP loop is CPU speed dependent while udelay() > provides a deterministic delay regardless of host CPU frequency. > > Signed-off-by: Piotr Zarycki Reviewed-by: Vitaly Kuznetsov Thanks! > --- > .../testing/selftests/kvm/x86/hyperv_tlb_flush.c | 15 ++------------- > 1 file changed, 2 insertions(+), 13 deletions(-) > > diff --git a/tools/testing/selftests/kvm/x86/hyperv_tlb_flush.c b/tools/testing/selftests/kvm/x86/hyperv_tlb_flush.c > index c542cc4762b1..4b7f089542c1 100644 > --- a/tools/testing/selftests/kvm/x86/hyperv_tlb_flush.c > +++ b/tools/testing/selftests/kvm/x86/hyperv_tlb_flush.c > @@ -141,17 +141,6 @@ static void swap_two_test_pages(vm_paddr_t pte_gva1, vm_paddr_t pte_gva2) > *(uint64_t *)pte_gva2 = tmp; > } > > -/* > - * TODO: replace the silly NOP loop with a proper udelay() implementation. > - */ > -static inline void do_delay(void) > -{ > - int i; > - > - for (i = 0; i < 1000000; i++) > - asm volatile("nop"); > -} > - > /* > * Prepare to test: 'disable' workers by setting the expectation to '0', > * clear hypercall input page and then swap two test pages. > @@ -169,7 +158,7 @@ static inline void prepare_to_test(struct test_data *data) > wmb(); > > /* Make sure workers have enough time to notice */ > - do_delay(); > + udelay(100); > > /* Swap test page mappings */ > swap_two_test_pages(data->test_pages_pte[0], data->test_pages_pte[1]); > @@ -189,7 +178,7 @@ static inline void post_test(struct test_data *data, u64 exp1, u64 exp2) > set_expected_val((void *)data->test_pages, exp2, WORKER_VCPU_ID_2); > > /* Make sure workers have enough time to test */ > - do_delay(); > + udelay(100); > } > > #define TESTVAL1 0x0101010101010101 -- Vitaly