linux-kernel - Re: [PATCH 4/6] KVM: selftests: Fix population stage in dirty_log_perf

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Date:   Fri, 15 Jan 2021 16:02:50 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Andrew Jones <drjones@...hat.com>,
        Peter Shier <pshier@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Huth <thuth@...hat.com>, Jacob Xu <jacobhxu@...gle.com>,
        Makarand Sonare <makarandsonare@...gle.com>
Subject: Re: [PATCH 4/6] KVM: selftests: Fix population stage in
 dirty_log_perf_test

On Tue, Jan 12, 2021, Ben Gardon wrote:
> Currently the population stage in the dirty_log_perf_test does nothing
> as the per-vCPU iteration counters are not initialized and the loop does
> not wait for each vCPU. Remedy those errors.
> 
> Reviewed-by: Jacob Xu <jacobhxu@...gle.com>
> Reviewed-by: Makarand Sonare <makarandsonare@...gle.com>
> 
> Signed-off-by: Ben Gardon <bgardon@...gle.com>
> ---
>  tools/testing/selftests/kvm/dirty_log_perf_test.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> index 3875f22d7283..fb6eb7fa0b45 100644
> --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> @@ -139,14 +139,19 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>  
>  	clock_gettime(CLOCK_MONOTONIC, &start);
>  	for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
> +		vcpu_last_completed_iteration[vcpu_id] = -1;
> +
>  		pthread_create(&vcpu_threads[vcpu_id], NULL, vcpu_worker,
>  			       &perf_test_args.vcpu_args[vcpu_id]);
>  	}
>  
> -	/* Allow the vCPU to populate memory */
> +	/* Allow the vCPUs to populate memory */
>  	pr_debug("Starting iteration %d - Populating\n", iteration);
> -	while (READ_ONCE(vcpu_last_completed_iteration[vcpu_id]) != iteration)
> -		;
> +	for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
> +		while (READ_ONCE(vcpu_last_completed_iteration[vcpu_id]) !=
> +		       iteration)

Same comment as earlier.  I vote to let this poke out, or shorten the variables
so that the lines aren't so long.

> +			;
> +	}
>  
>  	ts_diff = timespec_elapsed(start);
>  	pr_info("Populate memory time: %ld.%.9lds\n",
> -- 
> 2.30.0.284.gd98b1dd5eaa7-goog
>